Multi-target attacks can trigger revenge because you are also hitting other opponents.

And you have a shield.. which can deal damage to the other team entirely.. .so revenge can kick in.

(I realize the above may be stating the obvious for many)

But I do see that one hit by your Guardian which apparently stunned or had some effect on VHE... and triggered the revenge. I would wonder why the Guardian also hit VHE.... not why revenge was triggered.