TL;DR:
Some distributors have context-related descriptors for their movies:
Disney for example says NO to new characters smoking in new films, but if a historical figure is portrayed smoking, because it was what they really did back then, then it gets a "historical smoking" descriptor.
(Following criticism from senators and pressure groups, the group responsible for the rating systems, MPAA, announced a shift in policy in 2007 to consider the use of smoking when rating films from then on. That policy has been updated since then to include anyone seen smoking in films, and the descriptors used showed added context (ie. 'historical' for period-relevant smoking depiction)
The following does give light to where the meaning comes from and its distinction form normal smoking: https://www.hollywoodreporter.com/business/business-news/alan-horn-talks-disney-fox-merger-streaming-pixar-post-john-lasseter-1187054/
With Fox, we can make movies that right now I say no to. Take Bohemian Rhapsody, which is PG-13. It’s a hit movie and very, very good. But there’s no way we could make it under the Disney label because the characters smoke cigarettes and other content. Nor could we have made [Warner Bros.’ R-rated] Oscar-winning Argo because the characters smoke and use the F-word.
We always have to think about the smoking policy. The audience for a Disney movie may not know what they are going to see, but they know what they aren’t going to see. There are certain things we just can’t include because we’ll get letters.
So, smoking and bad language, that explains why we don't see those in the films.
However there is a caveat to the smoking ban if it is period accurate!
Speaking at the Disney shareholder meeting in 2015, executive and former CEO of Disney, Bob Iger, said: "We are extending our policy to prohibit smoking in movies across the board: Marvel, Lucas, Pixar and Disney films.
"In terms of any new characters that are created for any of those films, under any of those labels, we will absolutely prohibit smoking in any of those films."
However, he added: "Except when we are depicting a historical figure who may have smoked at the time.
"For instance, we've been doing a movie on Abraham Lincoln, he was a smoker, and we would consider that acceptable."
https://www.mirror.co.uk/film/disney-films-ban-meaning-you-23548771
The Motion Picture Association of America has announced that, along with swearing, sex and violence, smoking on screen will help determine what audience-rating a film receives. The MPAA says it will consider how much a movie glorifies tobacco use, and who's doing the puffing. The movie board says they will weigh historic context, as well.
https://www.npr.org/templates/story/story.php?storyId=10141697
MPAA Chairman Dan Glickman said his group's ratings board, which previously had considered underage smoking in assigning film ratings, now will take into account smoking by adults, as well.
Film raters will consider the pervasiveness of tobacco use, whether it glamorizes smoking and the context in which smoking appears, as in movies set in the past when smoking was more common.
Descriptions on sex, violence and language that accompany movie ratings now will include such phrases as "glamorized smoking" or "pervasive smoking," Glickman said.
If rated today, a film such as 2005's "Good Night, and Good Luck," about chain-smoking newsman Edward R. Murrow, would have carried a "pervasive smoking" tag but probably would have retained its PG rating because of its historical context in the 1950s, Graves said.
https://escholarship.org/content/qt5sr9w2s1/qt5sr9w2s1_noSplash_8e29988a7d738adc7ad7c334a752c557.pdf
Are MPAA’s tobacco labels
protecting movie audiences?
The MPAA has never used the phrases “pervasive smoking” or “glamorized
smoking,” as it originally proposed. Instead, it has either used “smoking,” with nothing to
indicate the harm potential, or modified “smoking” with terms that minimize or even
justify (“historical smoking”) the film’s tobacco content.
Overrated? It’s a PG-13 world; we’re just living in it
Drug use, teen drinking and even smoking can give the MPAA ratings mavens the conniptions. “The Imitation Game,” another decorous period piece, was tagged PG-13 because of “historical smoking.”
https://eu.galesburg.com/story/entertainment/movies/2015/08/13/ben-steelman-overrated-it-s/33685140007/
https://www.backstage.com/magazine/article/mpaa-adds-smoking-film-rating-factor-29444/
https://www.cnsnews.com/mrctv-blog/eric-scheiner/warning-historical-smoking-and-e-cigarettes-are-visible
Smoking Makes a Cinematic Comeback
Smoking also raises ratings issues in movies. It was seldom seen on TV for a while (TV ads for tobacco products have been banned since 1971) but has returned with vigor, especially on streaming services. Some historical figures, such as Winston Churchill with his cigar in Darkest Hour (2017), would not seem accurately portrayed without their tobacco products.
These widely accepted, but not universally true, ideas about how much people used to smoke in the old days have given rise to the interesting MPAA rating description “historical smoking.”
https://publicsquaremag.org/media-education/for-mature-audiences-only-relabeling-crass-media/
The linked PDF also includes a list of various descriptors applied between 2007-2010:
https://escholarship.org/content/qt8hn866tt/qt8hn866tt_noSplash_7901ea31c2ee8889a48bd25c4fdde316.pdf
- not many include "historical" smoking, but at least one does where the real-life characters portrayed are still alive (as of 2022).