Possible bug with Piranha?

[Sumia]

I had a really good run going with a fluff and piranha cycle and I got a perk that minimized things randomly. Well, one of those times it minimized the piranha and he zoomed out of the tank on his own.
He's done this before, and when normal sized it attacked the enemies and killed them for me without me "playing" anything.
This time however the mini piranha attacked me as if I were an enemy instead. I took the full stack of fluff damage killing me instantly at full health.

Is this a bug or did I just luck out the first time the piranha did it?