I think with these kinds of suits the core conceit is that gun manufacturing/sales is a sordid, immoral business along the lines of cigarettes, and that the very existence of a consumer market for their product implies their misuse and negative impact on society. Therefore, they should bear more responsibility for that impact.
They were emboldened by the suit against Bushmaster/Remington that succeeded and ultimately bankrupted Freedom Group.
My understanding is that the drill is fixtured in position in procedures as delicate as this, so that it really can’t move and drill anywhere except where it needs to. Likely why Dad thought (wrongly) that it was harmless.