Keep your eye on crazy uncle Joe. He will spill the beans, by word or action. But I think Barky wants to get past the impeachment kill zone.
Another possible explanation, not one that I’m necessarily sold on, but in the interests of considering every logical possibility:
Obama is in professor mode, thinks we care about his opinion on this weighty issue, and this is his opinion, it may mean he thought Clinton would lose anyway, or it may mean he thinks she will win anyway.
Therefore not really a “tell” about anything, just the professor holding court for his grad students.