I don’t know what PhD program your brother was looking at but ideally candidacy committees won’t pass you unless you chose the problem or made it your own. Where your brother is right is that forming such a ideal committee is mostly politics.
I mean, if you're interested in astrophysics, you shouldn't go to a school where the Physics department is focused on nuclear physics!
He didn't care about the status of having a PhD
He didn't need a PhD to advance his career
He was having fun doing math stuff anyway