Don't overlook the conversation Zoe has with Noah in 2016, but that scene was a very ambiguous clue that could have meant anything. I mean, Noah could have been an ordinary human with access to Manhunter technology—or he could have been a Manhunter himself, which amounts to exactly the same thing.
What makes this plot twist not entirely convincing to me is that they hold him responsible for Sinestro’s release in a way that was never actually explained.