Pitch has nothing to do with stall, every student starting out gets taught that. In a severe up draught you could be pointing nose down, and still stalled. It is the angle of relative airflow to the wing. Just like a power on stall pulling out of a loop, low angle of attack relative to the horizon, but still a stall.
If this was indeed a very severe up draught, the plane could very well have been in an immediate stall.