Healing Word in a Higher Level Slot — is it still a Bonus Action to cast?

If I prepare healing word in a higher level spell slot, is it still a Bonus Action to cast?

Related context

My DM cites Critical Role as evidence that this is probably not the case because in all the hours he’s watched them play their 5e campaign, they have ruled healing word in higher slots as not a Bonus action.

I’ve not watched Critical Role, so I don’t know if this is even the case in the show.