The problem is that (at least where I live) in English people say "the food is good" 100x more often than people say "the food is tasty" when they mean the same thing. While "tasty" might be a better definition of the word itself, "the food is good" is probably a better translation of the phrase. Also, for learning it's one thing, but for testing out of a level, it's quite a different goal-the program should want to know how well I know the language, not whether I know that one particular word (which it's obvious I do, anyway, from my answer.)
The way I see it. In terms of food, the two words are technically synonymous but the problem is "good" is a very general term that can mean anything positive in the English language and they want you to know that טעים is to be used for food only and טוב can be used in other situations such as בוקר טוב or הספר טוב.