Explanation: https://twitter.com/tyronestash2/status/1723604810317156638

So the guy just clips through the fence, and his dog swaps to a human model (still with dog texture) to climb over the fence...

Modders were so dedicated to bringing the Fallout experience to PZ they even added their own glitches.

The limitations of game's engine, really. The modders can't add dog jumping custom animations, so they defaulted to the player vaulting animation.