Any opinions on what may have caused this?

The ball/tip came off.
Happened to me, 2 or 3 pushrods..ball ends came off at the lifter. I was unbelievably lucky that the ball ends landed on the valley and didn't get home run'd by the counter weights through the block or into the cam lobes.
Some companies, for a min.. some still do.. electro weld the ends on... bad idea.
I lost a cam lobe from the lash opening to 1/4 and the lifter slamming it over in over