If he was actually using it as a crutch, with the stock under his shoulder, Yes. Perhaps he was actually using it as a cane. Maybe mfrs could start marketing crutch ARs for the aging get-off-my-lawn population, and bong ARs for young, white libertarians, AR barbecue tongs for exurbanites, etc.

The ergonomics are mostly compatible with his excuse for his stupidity. If he leaned well forward to stand up he would likely grip the weapon at a lower point and his weight would be pushing down in the direction of the trigger travel. Still, the rifle almost certainly had a trigger guard and so the trigger should have been protected if his hand slid down.

 A more likely scenario to my imagination is that he was a tired old fuck and was holding the rifle in one hand like a pistol and pointing it up as he strained forward to stand and he accidently tightened his grip and fired a burst on automatic. If it was part of a forensic science show the brilliant detective might notice either marks on the floor from recoil if his story is true or the absence of them if it is bs. Or, the floor might be carpeted or the rifle butt padded. Any scenario that I can imagine includes him being an idiot whose idiocy cost another person their life. Manslaughter for sure regardless the truth.

I'll have to remember that one the next time I'm having a discussion with my in-laws about the topic…