MF:
The IG”M is talking about there where the resturaunt is mixed, kosher & non kosher. There, one can not enter because someone will think the person is eating the traif stuff, or that the store is Kosher.
Here, we are talking about a well known non-kosher resturaunt (in which no one would have a Hava Amina that it is Kosher) where you can buy a soda. As I said, if the guy is holding a burger, it would be MA.
Nireh B’aynai, that if there would be a Safek (such as Dunken Doughnuts or Subway, which some are Kosher), it would be more of a problem, and perhaps the IG”M would apply.
It is a good Mekor though (and very much Nogaigh in other cases), and I thank you for pointing it out to me. This is why I stay, to learn.