No idea what they base their rankings on but it appears to be statistical over opinion (which is what Stein's ESPN power ranking is) since they mention point differential for POR.
C's are now in the top 10 in point differential and have the number 1 defense (based on points allowed). Their last 10 record of 9-1 is also tops in the league at the moment. Can't really argue with the ranking right now. But let's see how thing stand after LAL and CHI coming up.