I mean, he wasn't exactly wrong. He knew it was a new Pokémon, but was mad at Niantic for pushing it to the game early and having it leak before its reveal.
That can't really be helped, though, and that's the part he was wrong about. The way Pokémon GO works, it refreshes in-game assets from the server when the game starts up. In order to get everyone to see a new asset, Niantic needs to push it ahead of time so that everyone gets a chance to restart their games at some point before the asset is activated. Even then, there are still dingbats who run the game nonstop and never close the app, which is why a few people were seeing Kecleon instead of Meltan (because Meltan occupies Kecleon's slot and those people's clients still had Kecleon's assets cached).
He was still one of the first to publicly realize that it was an intentional push for an imminent event and apologize for his earlier comments, so I don't fault him. There was a lot of hype and confusion going on that day.
