It's a match up thing wouldn't read too much into it.
Yeah this is what ESPN says:
Spin: Noel is the usual starter for Philadelphia but is being benched in favor of Robert Covington to take advantage of a lineup change made by Indiana. Noel isn't likely to see a minutes reduction off the bench, he'll simply play with the backups to start the game.
Noel has struggled a bit at the start of this season, though. He finished last season averaging 14.3 points, 11.2 rebounds, 2.1 blocks and 2.4 steals on 50% shooting. in March... and so far this year he's averaging 11.6 points, 9.4 rebounds, 1.3 blocks and 1.8 steals on 40% shooting... I don't know how much of that is him trying to play out of position next to Okafor, or the fact that he missed a couple games recently with sore wrists or what, but he hasn't looked as good. Philly should trade him for a quality PF like Jared Sullinger or Kelly Olynyk who would look better next to Okafor. Sell high, Philly... before he regresses even more! lol