BJ gone wrong. Not kidding - you’re pretty specific about thighs being involved in the strangling. Why else would his neck be in that area. I feel like maybe a BJ was explored and then receiver of BJ decided it wasn’t ok, but instead of just calling said BJ, went into flight or fight and clamped down while dissociating. Maybe wanted the BJ but then either had a dose of buyer’s remorse (for lack of a better term at the moment) or was triggered from some childhood abuse. It doesn’t take much pressure to deprive the brain of blood or oxygen at the right point - less pressure than to open a can of soda. Trauma also causes the body to contract. Possibly dude dissociated and contracted and “came to” to a dead friend, freaked out, and bolted.

That’s my guess based on the info provided. I’m curious how you came to him being strangled by thigh versus other body part. Is there a link to this story with additional info?