Infectious Sporeling + Animated Broomstick Bug

Hey,
Pretty sure this is a bug - please tell me if i’m wrong.

I played a game of Arena when i threw my full health Dragonmaw Skystalker into an Infectious Sporeling for my Dragonmaw to become the Sporeling. I then played my Animated Broomstick for my Sporeling to get RUSH but it didn’t. Shoudn’t it?
All of my Hearthstone experience told me different when i planned the play, but I could be wrong? Please Help

Thank you

Were there any enemy minions remaining on the board?

Yes. I tried to rush the sporeling into an opponents Lake tresher

there was a similar question a few months ago about sporeling and rush that basically concluded that sporeling might work different from other cards in the game