The "numerous online reports" are not true.. Your understanding is much closer.
Let's start with the obvious - you cannot be in violation of US immigration overstay rules when you are not in the US. The US cannot and does not enforce this.
The actual rule is very simple. If you re-enter the US less than 90 days after having been admitted on a VWP, having visited only Canada, Mexico and the adjoining territoryCanada, Mexico or the adjacent islands, you will normally be readmitted on the same I94 and must leave 90 days or less after the initial admissionyou will normally be readmitted on the same I94 and must leave 90 days or less after the initial admission. That is all. Everything else that is said, like time in Canada "counting toward your time in the US" is just an approximation to try to explain the above.
If you spend a short amount of time in the US, then leave and spend time in Canada or Mexico etc., and attempt to return more than 90 days after the initial admission, you are eligible to be admitted under a new I94. Whether you are admitted depends on your circumstances, just like it did when you were first admitted. If you have spent only a few days in the US, and intend to spend only a few more, and have not in any other way made yourself undesirable, you are virtually certain to be readmitted. If you spent a long time in the US and only a very short time in Canada etc. then it is very likely that you will be denied readmission. (That is true even if you went somewhere outside the Canada Mexico Caribbean area.)
In any case you have not overstayed in the US.