........goddamn idiots.
He was trained by the first and second hokages to be their successor. He trained his ASS OFF to be able to use all the base elements. He studied his ass off to know all the jutsu left for him.
It's hearsay. Just because some people say that he knows all jutsus in the village doesn't mean it is true. And the ability to perform Bloodline Limited Jutsu is out of reach. So the statement is false. He may know all the jutsu, but can not perform some of them. He can not perform Sharingan Exclusive jutsu. He can not perform Byakugan exclusive jutsu, except for copy the gentle fist in some way (as it's a taijutsu, anyone can learn to perform it. But they never will be able to block off tenketsu without the ability to see them). And at one time Kushina was a part of Konoha, does that mean Hiruzen is able to perform the Chakra Chains like she does?
Need I go on? That belief is false...