Interesting. It's likely the point of constraining the graduate course to grad students had nothing to do with their maturity. But you see what you think is a sign of immaturity, and turn the constraint into a maturity filter.

I'm quite grown, and I wonder about the ownership/control of the cluster and why he didn't simply lock the professor out entirely, contingent on the approval of his waiver.

If anything, doing something as small as lowering the priority of his jobs instead of brazenly stonewalling him might be the sign of immaturity.