They were trying to read BO health care bill...
I smell a sex scandal. What other reason would there be for such secrecy? Perhaps a little mile high action distraction?
My considered opinion is that they (the pilots) miss-entered the destination and route number (enroute waypoints associated with this flight p[lan) in their flight management computer (FMC) and thought they were flying to a different airport. Typically, this is a joint checklist item for both pilots to confirm destination and route of flight and proper FMC entry.)
To complicate the matter, I think they missed a radio change and didn’t respond very quickly to the silence on freq. Ergo, no prompts from ATC. Bad combination of errors.
Once they were back in radio contact, they were informed of their deviation and then had to do an enroute change of destination and a re-entry of waypoints in their FMC to return to MSP. That takes a little bit of time, as it isn’t a task that is done very often. It’s only performed during reroutes and/or and diverts, which are actually pretty rare.
I think this is the only plausible explanation. If the pilot flies past his “clearance-limit” ( as in the destination entered in the FMC) and the aircraft is on autopilot, the autopilot will disengage. This would be accompanied by aural warnings and flashing lights. It would have been the attention-getter that these guys didn’t get.
IMHO.