Humans without experience with either sport could potentially run into the same difficulty distinguishing them. For instance, how would one tell the difference between Aussie-rule football and rugby based on a picture?
But my point is, if the network believes with the most confidence that this is tennis, shouldn't it answer it's not soccer in the next one? Or at least with a hugely less confident answer? The fact that it answers like that makes me think it is not a very stable source of question answering.