Dungeon Deserter debuff - but entered dungeon SOLO. Not in a group/etc

Am… Am I mistaken here? I got a weekly Dungeon quest and hastily flew over to the dungeon entrance and entered the dungeon, 100% solo. Just me. Myself. And I.

Quickly realized I was in the 5man Mythic dungeon, solo, and ported out. Oops on me! Will re-Q as follower to bang the quest out. But then…

Ended up with the Dungeon Deserter debuff once I ported out? Debuff literally says “abandoned your group and must wait before using Dungeon Finder or Raid Finder again.” I used/did neither… There was no group to abandon. I’m a nice guy! I’d never…

This can’t be right. Did I miss something? Has this always been the case?

On the bright side - 5min left on the debuff, while I typed this rant.