Back to semantics but I guess, but that depends on whether "not being 100% sure" = "a mistake".
Unless the referee comes out and explains why he didn't give it then we'll never know for sure whether he (a) saw clearly what happened, and thus applied the rules incorrectly, or (b) whether he couldn't see clearly what happened and therefore was duty bound to give the benefit of his doubt to the keeper. That said, if the answer is "(b)", I guess one could argue that his "mistake" was not being in the right position to have a more clear cut view of the incident.
Anyway....about time we got back to gloating about the 8-0 win. My grin is still as wide as it was on Saturday!