They were cruising at M .80 at FL350 so how much static pressure change with a climb would it take to go above mach limit with a blocked pitot tube? I don't know but am trying to understand why they pulled up into a deep stall.
Something must have spooked them. I don't think just losing AS would. Maybe the stall warning going off again at the latter part of their descent and pulling back into a deep stall to silence it also caused them to pull up into a stall as the overspeed warning sounded. The guy flying was pretty new on the aircraft.