Android 17 and 18 Kill Dr. Gero
The future Androids 17 & 18 kill their creator Dr. Gero, much like they did in the Android saga, except without 16 or any of the Z warriors present.
This scene happens in the alternative timeline where imperfect Cell took Trunks' time machine to travel to the past.
I'm guessing that they're the same androids from the 'History of Trunks' special...