"JG" wrote ...
My WAG is that he probably bought it due to down drafts
in strong wind in mountains.

Was he operating on the windward side of the ridge? Locals reported some
clouds over the ridges.

My WAG:
He gets into hard updraft, cuts power, noses down,
ASI increasing, still climbing, noses over more,
VSI still positive, ...oops now he's in IMC,
......the ASI is in the upper yellow, ...damn this cloud,
......Oh Sh*t .... the VSI just swung around to -2K,
......BANG!

Not the first, ... not the last.