Rampage's ultimate involves teleporting to an enemy hero and involves a short period of waiting time before the teleportation actually occurs.
One of Ophelia's abilities is a near instant (if not instant?) teleport that can be used to teleport an ally back to the base.
In this case, Rampage began his ultimate before his target was teleported back to the Legion well. By the time the teleportation was finished, his target was already in the well, surrounded by creeps... This was the result.
By no means is this video meant to insult the unfortunate Rampage, as this all happened by pure luck and unfortunate timing.