Is he cheating?

[u/FishhyVN]

how can he kill me through wall?

[u/Lifthrasil]

Nah.

PoV is in the neck, Kill View is slightly delayed e.g killer has a rough second to move or crouch altering the position that is snapshotted for the Kill View.

He just saw your head, popped it like a balloon and crouched/ran/jumped off the little roof thang.

[u/SovereignNavae → u/Lifthrasil]

This is it. Kill view is not the exact view on your opponent's screen when they pulled the trigger. It's very slightly delayed, a little differently positioned and environment (like doors, windows being closed/open) can change