Put it in perspective. Your friend applied for this job. He asked for an interview. They accepted. They made time for this apparently long process where they determine if he's a fit for them. In the middle of this, he stands up, announces the interview is over, and asks to leave. That's their line. He basically just turned the entire interview process around, and rejected them, putting them on the very uncomfortable "wrong side" of the interview desk. They're supposed to be the "in" crowd and he's the "outsider"; they should be rejecting him at their option. And there are more of them than there are of him to be thinking that way.
I'm not saying any of this is the right way for a potential employer to be thinking about the process, but I am saying this is probably how they were thinking about it.
Personally, I agree that interviews are two-way; employees should make themselves look good to employers, but the same applies in reverse. This may actually have been a contributing factor as well. The interviewers may have gone to some lengths to show your friend what they liked about working there. Devs wearing what they want to, working in a nice big open space as opposed to being buried in cubes behind file cabinets, people challenging themselves outside their job.
In short, the ideal "programming outside the cube" environment, which (in their opinion) any coder would jump to be a part of. Your friend rejected all that. If I were still a 20-something coder in a casual environment like that I would be shocked and dismayed too; it might even come across as a rejection of my lifestyle as a young coder.
