Seniority, in some companies, is how long you've been at your current title compared to other people with that same title. It has nothing to do with either of the things he mentioned. Then there are the "senior" titles. But there are a number of "senior" titles that are junior to other non-senior titles. All I can say for sure is that there are a lot of interpretations of the word, and saying that it is one thing and isn't another is really just saying, "When I think of the word, to me it means one thing and not another." But that's just the vote of a single random blogger.

Maybe what he meant is just that, "Having a higher title does not necessarily mean that you are qualified to work at every company at that title."