That comment states that TensorFlow does not handle a large number of operations well, not a large number of variables. There's a large difference between those statements :). But yes, the general point is correct, especially for models that do not use many matrix multiplications.
Oops! Right you are. I just recalled that there was some issue with a large number of <insert important item for MCMC here>. I should have reread the threat before linking it.
