it states moshiach who is the rebbe of the generation (and as we are the generation of moshiach it’s the rebbe) knows Torah more than Moisheh – you see Moisheh certainly conveyed the laws, but Moshiach being the level of malchus – receiving all the wisdom of every sage, all the Torah, all the Divine inspiration (and though it states there was no greater prophet, this refers only to the depth not the scope, see shoftim nun bes)