Normally, lifters come apart like that because of too little preload that allows the plunger to come up against the retainer and push it out. If you have a non adjustable valve train, that would point to pushrods being too short.
Don't think that's it in this case. You can see the deformation of the retainer where the rod pushed down on it. I have Harland Sharp adjustable roller rocker arms that have been working for years. This is a case of:
1. Fixing something that wasn't really broken just wasn't "right" in my view but worked. (mistake number 1)
2. operator error upon installation. (number 2)