In the absence of any other obvious problems with the valve train, that type of failure is usually indicative of a valve sticking open. It usually does happen with the exhaust valves (you know, due to carbon build up on the stem).
When the valve train is functioning properly, there is never a gap between any of the components. The valve spring is always under some degree of compression. That force of compression is transferred back against the valve stem via the keepers.
With the top of the stem pushing up against the rocker on one side, and the cam lobe (via the push rod) pushing up on the other side, there is no end play in the push rod. A zero clearance condition is always maintained.
However, consider what happens if - for whatever reason - the valve spring fails to return the valve to it's seated position:
As the cam continues to rotate, the lobe moves away from the lifter face. The lifter, due to it's own weight (and the weight of the push rod) will sometimes drop down into the lifter bore. The push rod falls along with the valve lifter.
Meanwhile at the other end of the train, the stuck valve is preventing the spring from decompressing and forcing the stem upward against the rocker. The lifter has continued to fall in the bore and is now on the heel of the cam. The push rod follows right on down with it.
You get the picture - eventually a gap develops between the top of the push rod and the rocker arm. Without any pressure to keep it in place, the rocker arm is free to move anywhere on it's pivot.
Many times, if you are lucky, it will just kind of stays put. Or, if it does move, it stays within (or close to) it's normal - straight up and down - range of motion.
However, if the rocker rotates (as opposed to moving up and down) while it is free to move, that is when things turn bad.
By this time, the cam has made a complete revolution and it's lobe is starting to push upwards on the lifter face. The lifter rises in the bore and forces the push rod up.
If the rocker has not rotated out of it's normal vector, and is still lined up with the push rod, the top of the push rod comes up and finds it's seat in the rocker arm. The other end of the rocker pushes down on the top of the valve stem. Often this contact is enough to break the stuck valve free. The spring is allowed to decompress and re-establish the zero lash condition.
But if the push rod seat in the rocker arm has drifted out of it's normal spot...when the tip of the rod comes up, that is when all hell breaks loose.
Sometimes, there is no damage done. The push rod might hit in such a way that it just shoves the end of the rocker arm over to the side and out of harms way (that looks like what happened in your case).
Other times the rocker can hit close in towards to pivot point. If it contacts the underside of the rocker close enough to the pivot, it will get bent.
This is common in marine engines. The raw cooling water leaving the heat exchanger is injected into the engines exhaust and they both go overboard together. Due to various reasons, this causes the stems of the exhaust valves to be exposed to hot salt water and it is not uncommon to get a sticky exhaust valve near the point of injection.
Wouldn't hurt anything.
I don't mind a bit you used the same pushrod with the same rocker arm, but it's not necessary at all. The push rods and rocker arms don't usually create a DNA type wear pattern. Lifters and cam lobes for sure on flat tappets. I'd keep them matched up, but for roller cams and lifters, I don't think it even matters. 
