either establishing evil dragon temples work on different principles or he must have deceived a LOT of people in the past for the sake of his temples...or I suppose he could have had a cult...never underestimate the power of stupid people in large groups, and the dragon could easily have taken advantage of such power if he had someone smart and/or loyal enough pulling strings behind the scenes
admittedly the evil dragon temples working on different principles is rather more likely than variances in overlapping world mechanics I've seen from other series lately, but, still, given they seem to work otherwise on the same principles as the "good" dragon temple does, there is a decent chance they work the same in all aspects aside from which specific dragon they empower