Let's be serious- Cal doesn't get a lot of "steals". What he does, though, is scout really well, meaning the guys he recruits generally turn out to be as good or better than advertised. You haven't seen too many situations where a guy comes in with top 10 accolades, and then struggles to make an impact.
Matthews might be the rare case where Cal signed a lower-rated guy, but that seems like a scouting overreaction to Matthews' spring/summer struggles, not Cal plucking a hidden gem. Matthews was consensus top 10-20 when he committed to UK, and the idea that he was actually 30-50 spots worse than that after a few months of AAU play always seemed off. It seems even more off now that he's proving himself to be the best player in the state of Illinois, in one of the strongest HS basketball cities in the country. I suspect he'll creep back up into 5 star range when scouts do their final rankings. He might even end up on the Mickey D team.