Why did this arena match start off uneven?

why did the game start a 4v3? I have seen when someone lagged out before the match started, but it always shows the gamer tag when that happens. This match literally started out uneven. Why?

https://www.halowaypoint.com/en-us/games/halo-5-guardians/xbox-one/mode/arena/matches/3af55c33-3487-4e13-845e-7d94c7e899fe/players/b18tunerdaniel?gameHistoryMatchIndex=0&gameHistoryGameModeFilter=Arena

lazy link

Someone probably force quit their game because they meant to back out before the game started. They probably closed Halo while it was loading so they were never technically part of the game.