Well, the idea behind this theory is this. Engines burn fuel. Fuel
causes heat. Heat needs to be dissipated into the air (air btw, is the
only place it can ultimately go). As you climb there is less air. Heat
that was made with the more dense air some time ago needs to be
dissipated by less dense air now. Less dense air cannot dissipate as
much heat. Get the picture? We see steady state example of this in
overheating turbocharged piston engines that can be pushed too hard at
altitude. This climbing one is a little more complicated because it
involves changing air density, but same basic idea. The heat collects
in the engine. The cooling is designed for air density only so much
less than the air density that made the heat. Exceed that and you
overheat. The overheated engines seized. Climb at the rate the engine
is designed for and this wont happen. Could only climb that fast
because they were empty.

It's just a theory so far as what CAUSED the accident, but this
behavior is well known.