Valkyrie ult recharges from knockdowns

I am not sure if it was a bug, I just couldn't find an explanation.

I used ult on Valkyrie, landed on top of a team, killed them all and had ult again.

Watching the replay, I noticed I got 30% charge for every knock, and also around 10% charge when breaking one of the enemies' shield(the ult icon was getting an orange animation when getting additional recharge).

I checked in legend locker the abilities of me and allies (Lifeline, Wraith) and none of them mentioned something similar (also, they were still white evo anyway).

I thought I missed some important patch notes, but played more games and got no ult recharge in similar condition.

Does anyone know what happened?