Raid lockout question

This topic has been beat to death I know but I had a disagreement with someone on how lockouts work and just would like a better understanding. Issue is as follows.

Raider was a part of BWD 10M Normal. He left with 5/6 and did not kill Nef.

Raider forms NEW group, AFTER the old group had replaced him and killed Nef.

Raider checks to see if Nef is up. He is.

The person i had a disagreement with says “Nah. They must not have killed Nef.”

Why would that even make sense…? It’s not like YOU killed Nef… A bunch of other people did it without you being there.

what is the question

I think if any heroic mode boss is attempted, Nef wouldn’t have been active. I think the only reason he was alive was that the prior group only did normals.

Heroic lockouts are much more restrictive in that sense.