I'm still kind of skeptical that the pilots could be completely oblivious about it though. You'd think that if something is serious enough for a flight attendant or gate agent to call law enforcement, and get them onto the plane, then they'd tell the pilot about it too, if only as a courtesy or practical measure so they're not surprised about the noise or banging on the door. Also, at some point the pilots are going to have manifests of passengers vs crew, and that would change, so you'd think they'd see that happening, since the plane was fully boarded it seems possible they'd have had the first manifest, and wonder about / be annoyed about late changes. Or, maybe they'd simply see the law enforcement folks get on, or hear the call on the intercom / radio, etc.

I'm more inclined to think that the situation was misrepresented to them ("we have an unruly passenger, but we're taking care of it"), and they took it at face value without asking any questions. Will be interesting to see what comes out.