They give us the fifth best chance to win the finals? I have a hard time believing that
It's not that unbelievable when you think about it. The top two teams, by a wide margin, are out West in the Warriors and Spurs. So if you're a Western conference team who wins the title, you're likely going to need to beat both of those teams, without home-court advantage in either series. The road to the finals is a lot easier in the East. You have to go through Cleveland (which the computer is underselling slightly due to Kyrie's injury). But after that, the Celtics looks as good as anyone else on some days. Having a 3% chance to win it all isn't saying all that much, and a lot of other teams have a 2% chance. Really, it's saying "how likely is this team to make the finals, and then how likely is it Stephen Curry breaks an ankle?" It's not like the C's are seen as leaps and bounds ahead of the other East teams, and if we look at it next week should the upcoming games against Chicago, golden state, Charlotte, and Cleveland go poorly, we'll be back to 1% or less. It's just crazy in the East, with 2 games separating 1st from 9th and out of the playoffs, even 1/4 into the season. But when you look at point differential, which is often a good predictor of future performance, the Celtics grade out pretty well. And when you look at other things like roster depth, the C's are okay there too, and are able to withstand an injury or two without missing too much over short bursts (which is why we're seen as comparatively likely to make it out of the East.)