Polyarithmetic

(n) A person with a small amount of knowledge about a large number of subjects. Relates to a polymath (a person with a large amount of knowledge about a large number of subjects) in the same way that basic arithmetic (addition, subtraction, etc.) relates to mathematics (these and everything else in the field).

That guy thinks he knows a lot, but he's a polyarithmetic - two or three facts and he's done.