My default opinion of "vegan" items in menus of non-vegan restaurants is that they seem suspicious and are best avoided (I'm not talking about salads, of course). I tend to assume they are second rate meals put in the menu as an option for vegans who are there to dine with non-vegan friends.

I have been proven wrong on occasion, as some restaurants do offer decent options for vegans without specializing in it, but as a default intuition it seems more often right than wrong.

Vegan restaurants on the contrary can be quite good (again, with exceptions: just as there are bad steak houses or Italian restaurants, so there are bad vegan restaurants!). You just know the vegan items aren't an afterthought because every item is vegan.