Really busy right now so not much time to contribute here.
But to say it briefly: I don't consider creating (the concept of) knowledge a feat granting Arceus complete knowledge about all things or knowledge on how or perform every move in particular, especially not in such details.
Noah created the concept of knowledge and information, too, and is far from omniscient. There's really not much reason a being that creates the concept of knowledge would need to have access to all knowledge and Arceus has be depicted as not all knowing on several occassions. (e.g. the meteor movie or PMD against Dark Matter. Possibly others, too)