Sometimes you just aren't sure what something is. This usually doesn't happen botanically as scientists dedicate their lives to research plants, including obscure classification specificities.
Culinarily though, there is no strict definition of what is a fruit and what is a vegetable. People can sometimes disagree and cause no widespread accord to be reached. In such cases, all you can do is understand how the words "fruit" and "vegetable" are used and then reach your own conclusion about which you think is more fitting.