I agree with your assessment as to being the cause of the concave shape of / damage to the shaft.
We call them borer's. Since they bore holes in the chalkI'm sure everyone here already knows this, but almost all the players at your local pool hall or tavern are clueless.....
The people who drill holes into chalk don't know how to chalk. They are stupid as stumps. That technique does not get chalk on the tip well. Good players don't chalk like that. If you have a home table and your chalk looks like the typical pool hall chalk -- drilled down the middle -- you don't know how to chalk. And bad chalking can ruin your spin game.

I have a feeling this fella also has a chalk holder, and the chalk is way below the holder so the holder itself is scratching the shaft. A solid holder, plus chalk rubbing on the shaft coild work like sand paper.