I get that but that's not why it is not populism.

Science to a scientifically literate society maybe popular but it is not science because it is populist.

The point of a vanguard is to have social scientists guide the masses; the proletariat may hold reactionary ideals, residuals from capitalism/feudalism/slavery, but they are liberated through science.

Marxism is a science.

Social scientists cannot liberate the masses, the error of the Narodniks, only the masses can liberate themselves - the vanguard is just the tool used to achieve this.

Understanding this significance is partly how marxists can avoid tailism - Marxism is neither workerism nor populism though it may be popular amongst the proletariat, especially of the global south.