His ratings are a combination of a team's offensive and defensive efficiencies.
Here's a description of his system.
As for a reason for ODU being ranked so high, maybe it has something to do with one problem in the system (and Pomeroy acknowledges this problem), which is that it doesn't put a cap on margin of victory. Take a look at
ODU's results. Of their 8 wins, 5 have been by more than 25 points. And of their 4 losses, 3 have been by 8 points or less. On average, they've won big and lost small.
It's still early in the season. As Pomeroy says, "More games will push these teams to their rightful location."