We obviously weren't there but in the case of a failed or dodgy AH you still have altitude, VSI , ASI, P2 AH and I guess a Standby horizon.. That's a lot of instruments to confirm you are climbing..
Obviously, a 1g turn and the AH says it's wings level is a different story you trust the instruments.( not saying that's what happened in this case) . SP ops and aircraft not setup for MC probably just adds to the confusion by having a safety pilot.