Cockpit Stress
Knowing of the low overcast, if that pilots autopilot had this auto-capture feature, his motivation would have been to ease his workload and obviate spatial disorientation during transition into the clag. The effect of his action would have been to capture the airport elevation as target altitude. The TruTrak, at least, takes a few seconds to process and implement settings, so that the airplane would be expected to do exactly what it did: ascend into the clouds and a few seconds later return to the preset target altitude of the runway.