There really isn’t anything more to this than the backend team prepping to support the Twitch drop and accidentally pushing the “dispense” button for real for a few lucky randomly-selected accounts.
Oops.
TBH, this gives me hope that when the time comes to fulfill the drops for real, there will be no unusual delays like have been seen with the other drops for some folks – because the awarding software has been live-tested.
I don’t think the “awarding software” was used. I think all that happened is that those items got changed from regional WoW license-based to Battlenet-based.
When Blizzard did the backend update for the event those players had their Battlenet accounts get credited with it because they already had them on one regional WoW license. It’s possible if they had one they got credited with both the pet and mount because the two are awarded for watching four hours of a stream. I’ve had them both on my NA license for some time now. When this went through they showed up on my EU license too.