Saw this great tweet a few days ago. I can't link it right because twitter appears to be down for me, but it broke out the results of a playoff game based on how the series had progressed so far.
When the home team wins game 1, they win game 2 74% of the time. When they lose game 1, they win game 2 77% of the time. Pretty amazing, because to me at least, you would think if all you knew was the home team won game 1, that would be an indication they were the better team and would be more likely to win game 2, but not. (Also, fwiw, the home team wins game 1 about 73% of the time)
You see this throughout the series too, if the home team is up 2-0, they win game 3 43% of the time, but if it's 1-1 they win game 3 48% of the time.
The pull back towards even in these playoff series is really something. Chalk it up to whatever you want to. I am sure there are theories!