Mao is correct in saying that communists need to learn from the masses. He's talking about the Mass Line, an organizational tool to help keep the communist party linked with the masses and avoid tailism or commandism. However, that doesn't mean liberalism is correct, because there are more liberals. Mao also wrote Combat Liberalism, in which he talks about the necessity of ideological struggle within the party, and proper agitation among the masses to lead them to correct theory and practice, as is the utility of the vanguard.

In your quoted text, Mao is fighting those members of the communist party that shirked their duties and looked at themselves as above the masses, a small but relevant issue within the CPC at the time. He isn't saying to abandon Marxism or teaching about Marxism in favor of whatever is most popular.