There's also a difference between being wrong about opinions (like statements about the future) and being wrong about things that are factual while making a claim that presents itself as a factual assertion. While the nature of what he's wrong about is banal, it represents an extremely dangerous disregard for facts. That he would make up facts out of whole cloth (or fully believe such a poorly done study because it suits his ego) should be extremely worrying to everyone. You knock Obama for his miscalculations, but if Trump's belief formation process is so defective when it comes to the banal, false beliefs are guaranteed to plague his decision making when it really counts.