The upholding was about the CCP leadership, not about planned economy vs. market economy. So that upholding is not in contradictory of Leninism, and not related to Marxism.
An important development (and difference) of Lenin is that he advocate of the establishment of a socialist state surrounded by capitalist states and the survival of the socialist state can only be lead by a communist party. Marx did not envision such stage. He did not point out how to move from capitalism to communism at all. In his vision of communism, there is no state machine, therefor communist party is not needed at all. In Marx vision, communist party is only meant to lead the struggle to overthrow capitalist's state, it has no role in leading and ruling of the society afterwards. Marxism does not equal to Leninism. Marx was more of a theorist even though he was actively involved in actions. On the other hand Lenin, Mao and Deng were more of activists trying to do something unguided by Marx in a harsh reality.
Deng also said that now it is the early/entry-level (初级) socialism, there will be advanced level (less capitalist practice) socialism. So Deng is only acknowledging China's current lack of material base, not changing the ultimate goal of communism. It is not deviation (which would mean a different direction, different end goal), but an early stage (half in and half out) of socialism.