It depends. Officially, it's not a listed religion, it's a political orientation or movement. Practically, it IS a religion. In the latter case, we agree that quotes are not warranted.
It's a religion without a deity, other than a sort of collective consciousness said to be possessed by "the masses."
I think Marx believed it would become a state religion, with the state taking the place of a deity. When that didn't work (which took them many decades to figure out), they created other pseudo-religions, environmentalism and multiculturalism among them. These pseudo-religions all prescribe the same route to salvation, which is international socialism and the destruction of Capitalism.