Erm no.
Sure, it's sctupping sad that he does that just to get wins, but it's not cheating.
Surely it's cheating as he is breaking the no teaming in solo game rule?
You might see what I mean first
here then
here, though Window 10 DVR was glitching out at the time so it wasn't enough evidence for a ban.
They are literally crouching to each other on the same island and looting chests together, before (this might be hard to see in the second video as the recording cut out) they cross the same bridge onto the middle island of the 3 in a row (you can work this out by looking at where they were at the end of the first video compared to the second), wait for beside the other as they hit the last enemy off and then sacrifice.
It doesn't matter if they don't both attack the same person; just standing next to each other for 10 seconds I find is enough to get players banned.