"The term 'whipper' comes from the whipping motion a climber will take if an unskilled belayer cuts the fall short, limiting the dynamic stretching nature of the rope and causing a pendulum effect (often into the wall)"

This is incorrect. This has noting to do with the skill of the belayer.

An unskilled belayer cannot limit the dynamic stretching of the rope. Yes, they can lock off the belay in a less-than-very-dynamic fashion, increasing the forces on the climber, rope, pro, etc. But they can't affect the properties of the rope.

Further, pendulum effect has very little to do with the belayer. It has everything to do with the placement of the last piece of pro in relation to where the leader pops off the rock. It's the unskilled leader, or poor pro placement opportunities that are to blame, not the belayer. The only thing a belayer can do to avoid the pendulum effect is drop the leader. (I'd probably choose a pendulum swing over decking, thank you very much).

I don't necessarily have a good way to rephrase the sentence, but the sentence is wrong nevertheless.

Dynamic rope is rated by the UIAA to handle a specific number of whippers before being retired.

Dynamic ropes are rated to handle a certain number of UIAA falls, not whippers. There is no quantitative definition of a whipper, hence ropes have no "whipper" rating. A UIAA fall is slightly more gentle than the worst-case factor-2 fall. While probably not nearly as dramatic as a whipper, a UIAA fall puts significantly more stress on the rope.