It's quite possible he's got connections to the club teams in the region. Stanford has recruited the area well over the years and Illinois has as well (not so much for Washington). No idea if he was responsible in getting any of those kids to Stanford/Illinois, but it's possible.
Also, to the point about where he was on our list of choices, I don't think he's ever been the No. 1 assistant (let alone the head coach), which isn't stellar (though it certainly doesn't mean he can't succeed). I'm not 100 percent certain about Illinois, but he definitely wasn't the No. 1 at either Stanford or Washington (which just hired their No. 1 assistant for the head job after their most recent head coach left for Minnesota).
It's also interesting that Mansfield was at Stanford under Dunning for nearly 15 years, then went to Illinois for 1 year (2016) under Kevin Hambly, who then got the Stanford job starting in 2017 after Dunning retired. But, Mansfield didn't follow Hambly back to Stanford. There certainly could be a very good reason for that, but, on the surface, it's a bit odd.