I mean, it's a character trait for Spidey to blame himself for **** that's not his fault in any way, it's what made him become Spider-Man to begin with, 'cause it's pretty insane for someone to blame themselves for not stopping a criminal when he had no reason to do so at the time, so him blaming himself for George's death would be pretty in-character, specially since it was way more direct than Uncle Ben's death.