Learning works as both a gerund and as a participle, i.e. as part of a compound verb. So, Louis C.K. is correct. An example: "What were you learning in school if it wasn't grammar, Fiasco?"

Learning works as both a gerund and as a participle, i.e. as part of a compound verb. So, Louis C.K. is correct. An example: "What were you learning in school if it wasn't grammar, Fiasco?"