It is often the other hidden ingredients that are usually the problem.
If for example it was a vegetable soup. You'd assume that it would be vegetarian and many inexperienced vegetarians make this mistake. Just because the main ingredients are vegetables or of vegetarian origin doesn't mean that it is vegetarian. Beef or chicken stock is the biggest culprit in rendering a potentially vegetarian dish non-vegetarian. Similarly, if you said cream of tomato soup, I would instantly assume that even if it was vegetarian (above still stands with stock) that as a vegan (ok I'll include that I eat eggs from my own chickens only) it would not be suitable.
Now what if it was tomato and basil soup made with a vegetarian stock? Is it vegetarian or vegan? Well have the onions been cooked in butter, marg (it happens) or oil? Butter would make it vegetarian. Marg can go either way but more often than not contains dairy of some form, so still vegetarian. Oil. You'd assume that the onions cooked in oil we'd now be on firm ground but... The big but is what about the stock? A lot of vegetable stock cubes and especially bouillon powder contain a small amount of dairy (often whey protein). So if it contains dairy, were still vegetarian, if we pass this test and assuming the stock isn't home-made, then were vegan if no one adds cheese to the top...
Now you see why I don't eat out often. I have to ask too many questions because of that pesky but potentially fatal allergy to dairy proteins.
Even strawberry jam isn't safe... butter is often added add an anti-foaming agent. I only know this because it was the way I was raised to make strawberry jam (for some reason it was always strawberry or anything containing them, but never raspberry). Luckily I know you ask because we often purchase at the small town's fetes, farmers markets and the likes and once or twice they have actually ring the person who made out for me (much to our embarrassment) only to find out that butter had been added.
So jam could be vegetarian or could be vegan or neither if the vegetarian doesn't like sugar refined over animal bone char (beet sugar is the biggest culprit here, cane sugar is refined differently and luckily for me in Australia all Australian grown sugar cane is refined via fractional distillation. Using animal bone char in Australia was banned decades ago, though imported sugar can still be refined using it. )
