People are reductive by nature. Take a complex topic, reduce it to a single descriptor, understand it better. Maybe it's laziness, intellectually speaking, or maybe it's a timesaver–either way, it's not particularly helpful and it's mildly insulting.
BJJ? Fighting from your back. Boxing? Fighting with punches. Wrestling? Fighting with takedowns. Judo? Fighting with throws. Karate? Fighting for points. Catch? Fighting with submissions. It goes on and on.
That is fine for beginners. Broad concepts pared down. It is even fine for experts who don't have the patience to explain their art to someone making an inquiry. It is not fine for teaching, though, and also not ideal for training.
Take boxing, for example. Few martial arts are as taxing to the whole body as boxing. A good boxer uses his or her entire body to leverage both offense and defense. Only beginners and mediocre boxers live in their punches; the good ones know there is more to the execution of a punch than simply "hit and don't get hit." That is reductiveness to the point of ineffectiveness.
BJJ and catch are not just about fighting from your back or from the ground. These are kinesthetic arts that require an understanding of human mechanics and how best to exploit them with positions, postures, submissions, and sweeps. Again, reductiveness to the point of ineffectiveness.
Ask someone to describe what he or she does in an art and you will learn what that person values. Ask someone to describe what other arts are about and you will learn what his or her biases are. This is valuable because the former tells you whether a person is a worthy training partner and the latter tells you whether he or she understands martial arts.
You might not want to train with someone whose values in an art don't match yours or with a person who has a blindspot for other martial arts beyond his or her selected style. To that end, being reductive can help you instead of limit you.
Because you reduce the amount of time you waste on that person and that is always a good thing.