He was very stable financially at that time (considering the entire family, even more), so that's not the issue.

Real estate is easy: discover a gem, buy cheap, sell high..

Yeah, that's the passive kind, and it has its risks too, if the gem turns out not to be a gem after all, or if the situation changes that makes it less valuable. Not the active kind, where you rent it out.

However if he had chosen to buy BTC or alts with solid projects, he can still buy, go away for 3 or 4 years and then come back to it.

Yeah, I agree. But he didn't.