Did Alan Moore have a reputation for being angry around the time that THE WATCHMEN issues came out on the stands? I don't remember--there wasn't that much coverage of writers and artists back then. The only thing I knew was that he was British and maybe a hippy.
I think it was after, when the penny dropped, that Moore got angry. When he realized that DC was taking advantage of the contract to exploit him and Gibbons. But that realization would have come later in the 1990s when DC kept denying him what he thought should be proper compensation and respect.
I imagine it also bothered him that other writers tried to ape his dark turns on classic heroes, but without any more depth to the comics than that.
However, I think it's a fair criticism that while Moore didn't like others exploiting his work, so much of his work exploited what others had created before him. Maybe he thought he was paying them fair homage, but a lot of Moore's work either uses public domain characters so he's using the work for free and without permission or they are ersatz versions that he gets to profit from without compensation to the original copyright holders.