It isn't as hot as a real volcano. It isn't made of the same material. It isn't the same size. Gases don't exsolve (or bubble out) of the liquid in the same way. But gases do expel the liquid out of the volcano in both a real volcano and the baking soda-vinegar volcano. In both cases, the eruption is caused by gases increasing the volume of the "magma" (liquid plus gases) and thus expelling the magma.