Is it a mistake to talk about hobbies in a job application?
There is a time and a place for everything. When evaluating your application to determine if you’re going to be one of the half dozen or so people who might get on the short list, your hobbies aren’t going to rate very high in the decision-making process, unless they suggest that they’re going to pull you away from your work too much.

But I’d also rather not work with a potential colleague who is so focused on their careers that they give up being someone you want to work with. Having hobbies and interests that have nothing to do with your daily job make you a better person, and it’s something you can talk about during a phone or in-person interview. 

In the specific case you’re asked, then that means it’s something they decided they do want to know about and you should answer candidly.