He said... “is of zero risk to me but will come back to haunt Joe Biden and the Biden administration,”

Honestly this doesn't sound like he's acknowledging Biden as the next president. He was just being snarky to jab at Biden.

Trump does this often. He always goes off script and makes quite frequent gaffs and dumb comments.

Don't be like the left and get hung up on every little word he says. That's what the left does. he was just jabbing at Joe after it (25th) was tried on him.