Actually, if you rewind the video on Martial's goal, it's easy to see that the error was on the midfielder who was tracking Martial and for some absurd reason stopped following him once he passed it off originally.
Funny enough, Sanchez goal against us was quite similar. Fernandihno was the tracker, I think he got a bit banged up and couldn't stay with Sanchez or perhaps he was just tired. Either way, everyone ond their mother recognized the error laid strictly with Dihno. No one thought Mangala or Ota were somehow at fault.
Yet, these same people watch a similar sequence, with a midfielder failing to stay with his mark, but the conclude the "error prone Stones" must be at fault, seeing as he was closest to Martial when he slipped through.
This would be the equivalent of blaming Mangala or Ota (seeing as Mangala was tangled with the player who passed off to Sanchez) for Arsenal's 2nd goal. But no one did that. This suggests people can actually read errors correctly. But are often influenced (Consciously or otherwise) by the reputation bias.
This is not to suggest Stones haven't been culpable for any goals, but rather he is no more error prone than your averagely good CB.
Again I'll repeat, he is less error prone than any of our CBs, or at the least, no more prone to errors of judgment or action.
His biggest flaw is having a reputation of being Error Prone.