Thanks for that.
That cannot happen unless the valvetrain has severe issues--broken valve spring, valve sticking in the guide, excessive wear, bent pushrod, etc. The valvetrain for that lifter has to have some amount of clearance before the lifter can come unglued like that. Extreme RPM could do it if the valves "floated" because there wasn't enough spring pressure. But I'm guessing you weren't turning the RPM needed to float the valves if everything else is in good condition.
I see another lifter at the top of the photo with no pushrod. Of all the engines I've worked-on, big-block Chevys seem to be the worst for bending pushrods. The stock 3/8 pushrods are bad enough, but Chevy used really-crappy 5/16 pushrods on some engines. Moving from 5/16 pushrods to 3/8 pushrods also requires new pushrod guideplates to match the pushrod diameter.
I would identify the lifters that are damaged, or the pushrods that are bent. For example, the lifter where the snap-ring popped free, and the pushrod cup is out-of-position. Then examine the valvetrain for that lifter. Is the rocker in position? No excessive wear on the rocker's pushrod cup, rocker ball and pivot area, and valve-tip end? Is the valve spring and retainer OK--LOOK CLOSELY and PAY ATTENTION because sometimes broken valve springs aren't obvious. Is the valve tip mangled? Is the valve tip even with the others--all the intake valves at the same height, all the exhaust valves at the same height? Pushrod bent? Then, pull the spider, the dogbone, and the lifter to inspect the lifter roller and cam lobe. I'd probably just inspect ALL of them, not just the visibly-damaged ones. If you find damage anywhere...look at the mating surface of the part(s) next to it, too.
KEEP THE LIFTERS IN ORDER, and facing the right direction so they can be reinstalled in the same position as they are now. (Even if you replace some or all of the lifters, it's good practice to maintain the relationship between moving parts. You'd keep all the rocker arms in order, and mated to their own rocker balls. Keep the pushrods in order, and know which end is "up"...you get the idea.
IF the cam lobes are not damaged, I can imagine replacing some or all of the lifters, cleaning the lifters you're reusing ONE AT A TIME, and replacing some or (preferably all) of the pushrods--and I'd be using 3/8 pushrods if the engine came with 5/16--so new guideplates, too. What else you replace will depend on what wear or damage you discover during your examination, and a "wild guess" at what should be done based on engine mileage, which you haven't mentioned.