Actually, this is a fairly common situation when performance injectors are installed and the valves are not properly adjusted before the user nails the throttle. Almost always is user error because they failed to do routine maintenance.
It can also be bad timing of the injection pump if it is a VE or P pump engine, or a failing injection pump timing piston if it is the VP pump. If it is a CP3 (common rail) system, then it is improperly adjusted valves only.
Most simple injector replacements are done without checking the valve clearance unless the person requesting the service specifies and pays for such to be done.
The rockers are not removed during an injector swap.
When this happens it nearly always turns out to be a bent pushrod or broken lifter, and very seldom is a broken rocker or galled rocker shaft. What happens is the additional cylinder pressure from the richer fueling mix igniting drives a valve back into the valve seat and bends the pushrod or breaks the lifter, or both.
If it is a 24 valve, then I would also recommend using rocker girdles, if you can find and afford them, when installing performance injectors. The 24 valve is subject to this type of damage about three to one over a 12 valve.