There aren't many charts of pitching moment. But there are many that show the CP (center of pressure) movement. Either one shows that the change in values of both do not change suddenly or with any real variance of change in rate that would suggest any sudden force that would provide the necessary result, a sudden change in pitch.

To get a sudden pitch change should take a suddenly increased or decreased force from somewhere.

What is interesting about this sudden tuck behavior is that it occurs as the wing needs to provide very little lift and then less and less. At higher speeds, the needed CL lessens and lessens. Same lift, more easily produced with increased speed, less CL needed. And if you look at plots of cambered wings that show CP movement along with the CL slope. The slope is almost flat and also constant.

What does seem worth pondering is that the CP movement is usually around where we often locate our model CGs and moves aft as the CL is decreased. And the NP of the model often is in the same area just a bit aft the CG (or the sucker ain't up there flying).

Interesting stuff, this theory.