User blog comment:BenignSpirit/Did Toonami mistakenly celebrate it's 5th birthday on its' 4th?/@comment-37065436-20190719185453

Considering no one is on topic, I will speculatively answer your question: its possible that there was a massive oversight on DeMarco's side where they mistakenly assumed that the 5th Anniversary was in 01 as opposed to 02 and no one caught it until now.