Not only the CZ 455 Varmint
Thumbing bullets into the chamber is a practice that I've routinely done with .22lr bolt actions when sighting in and during light rifle and other informal .22LR matches.
When loading directly from the magazine and then ejecting without firing the bullet, it became evident that bullets can became deformed when chambered feeding with the bolt.
It's something to be aware of even for junior rifle competitors who shoot single shot rifles or for those who use single shot adapters.
The adapters don't always line up the cartridge to feed perfectly into the chamber.
Nicks on the bullets may or may not have much of an effect on accuracy at all.
Each rifle is different but sometimes it's better to be safe than sorry and doesn't hurt to thumb the bullets in.
It becomes 2nd nature and some guns with thicker diameter bull barrels have an even higher angle of bullet entry into the chamber when fed from the magazine.