Mindflayer instakill method on accident (i think)

Second room 3-1, i think i somehow marksman interrupted a stray (causing an explosion) when the mindflayer fley literally right by it while charging their parriable projectile attack. Ive tried to recreate it but the timing is I.N.S.A.N.E.L.Y hard.

Im not sure if thats what happened but i remember clearly it killed the mindflayer, cause i know explosions is a way to trigger the «friendly fire» method of instakilling it.

Lmk what you guys think.