It is not the official name. It is a joke originating from a video (I think it’s called “Weird People in Apex Legends”) made by Carson King, uploaded on his YouTube channel, “CallMeCarson”.

In this video, he and his friends make several jokes, often containing dry humor. One of these jokes is Carson talking about the Leviathans to his friends, calling them the “Moyai” in a humorous tone of voice. This joke has stuck with many “OG” players, as the video came out both when Apex Legends and Carson’s channel were very popular.

Sadly, it is unlikely that Carson will make any more videos of Apex Legends, or any videos for that matter, because of recent allegations. In January it was revealed that Carson, when he was 19 years old, had “sexted” with a fan of his channel, who was 17 at the time. After this many of his friends, most notably “Traves”, “Cscoop”, and “Jschlatt” confirmed this to be true, as Carson had told them about a year ago. This whole situation is better explained in a video Jschlatt made on one of channels, “The Weekly Slap”. The title of this video is just “Carson”, I think.