Hit points in Dungeons & Dragons explicitly represent heroic luck and divine favour as well as endurance and bodily integrity, so if you survive something that logically ought to have killed you because the GM biffed the damage roll, you are absolutely allowed to invent some bizarre coincidence that saved you.
fun thing to do in your d&d campaign: they only represent heroic luck and divine favor. make it so a level 20 character is the exact same physically as a level 1 character, but when both those characters fall off a cliff the level 20 always lands in a haystack.
The whole party’s out there Mr. Beaning their way through a fight with a dragon. The fighter just evaded its breath weapon by tripping over a skull and falling into an open treasure chest – the poor lizard can’t figure out what’s going on.