Some of these decklists are from the previous banlist, before the introduction of the new meta. And yes, aromage player was REALLY lucky if he managed to kog with this deck. Especially if you condider the fact the he doesnt run balance, meaning that he likely bricked hard. I still doubt that this deck actually went to kog from legendary 1.
All of what you said and I think at least some players especially with decks like aromage or other rogues are also disconnecting to not get losses to disrupt their win streaks so they don't have to start over in them.
It used to be that way a long time ago where it counted as a loss. Then Konami changed it so that it doesn't count as one because they got enough complaints from people losing to it due to their connections. The thing is that people started abusing "disconnect forgiveness" to their advantage.
I'm not completely sure about all the mechanics behind it if it has to have the right timing. You can usually tell when a person is doing it compared to a bad connection where it will usually take longer between turns and the "bad wifi" symbol flashing more until it finally. With intentional DC there will be more of a quick pause right before they do it when it looks like they will lose.