Yep, I read them as a probe because Biden has gotten suddenly combative when faced with the mildest of pushbacks in the past. Hey fat, dog faced pony soldier, push up contest challenge, etc.
Tactically I think he has to wait for whatever cocktail they gave Biden to wear off a bit to go after him for that reaction. The other possibility is that he thinks he can throw Joe off the whole time by going after him that way early.