In the case you're describing, the hypothetical person is going into the hobby for the wrong reason. The primary objective should be the hobby, if you happen to find someone you get on well with all the better.
So the original question is how people find relationships IRL (outside dating apps). Some answer just get a hobby. But then the same problem remains as you can see.
The same thing can be applied for working in an office. People do get relationships in an office but you would be a turnoff if you said you're looking for a relationship when applying for a job.
So for people looking for relationships primarily, what should they do outside dating apps? Or should they just repress their desire and live their life? If they meet one in hobbies or offices, great! If not, c'est la vie.
So yes, get hobbies that you are genuinely interested in, but cultivate ones that can be pursued in a more social way and that have a decent representation of the demographic you're interested in. Then be open and friendly, but don't actively look for romance. Get the rest of your life in order in that manner and it'll happen as a side-effect.
The problem of course is that it is easier done in certain cultures and environments than others. E.g. probably much easier in some slower university town in continental Europe than in some busy car-centric US city. Also easier if you have a more relaxed working life than a busy career with only barely enough free time to eat and sleep. And if people are generally are more open and social and are not all holed in in their apartments online.
Arguably, in a lot of the developed world the culture and the environment has become very unconducive for such things, especially in the last 15 years. Watching older European movies from the 70s, you can really see how much things have changed.