We have several Jewish people here at the office that keep Kosher. They routinely order waffle fries and a shake for lunch when we go to Chik-Fil-A.
Perhaps they aren’t kosher ENOUGH.
Years ago, while working in a hospital, we had a rabbi who was considered one of the great scholars (I wish I had copied down his name.) It was my job to supply dinners, and he refused all our kosher food, which was disturbing to me (I, of course, was worried about his health!).
His wife brought it in other days and on the Sabbath he simply fasted. They spent some time explaining it to me but what it came down to, was the food simply couldn’t be properly kosher.
Not bashing anyone’s standards, but some folks make allowances for things that aren’t really kosher. I suppose they’re just doing the best they can or the best they know. But I think it is important not to leave the impression for anyone who might be reading that fries (and possibly milkshakes) at any non-kosher restaurant are very, very likely not kosher.
There are all kinds of problems with anything deep-fried in a non-kosher restaurant because the oils tend to be lard-based or they might use the same equipment for cooking non-kosher meat or poultry in the same oil.