Look up the odds of winning one hand of blackjack, and look up the odds of a team coming back from a 0-2 advantage in a 7 game series without homecourt advantage to win. I bet they're close.
I'll go out on a limb and make the claim that it happens much more often when the series is tied 2-2 than in other cases. I'll also bet that it's more likely that there's a successful comeback when the team that's down is within 1 seed of the leading team, like 2v3 or 4v5 as opposed to 3v6 or 1v4. The fact that 1 and 2 seeds win out against 7 and 8 seeds when they're up 2-0 has a lot less bearing on the series in question than you realize.
Haha, what's that they say about statistics?
I'm pretty confident that anytime a team is down 0-2, the odds are extremely low.
I'm pretty confident that anytime a team has been down 0-2 and come back to 2-2, they still end up losing a large majority of the time.
I'm pretty confident that anytime a team, even if only separated by 1 seed, when lacking homecourt advantage, after being down 0-2 and coming back to tie it at 2-2, still lose the series a handy majority of the time. I bet they end up winning less than 40% of the time. I bet its somewhere between 25% and 30%.