Neoclassical economics is built on the assumptions of microeconomics that say that all government activity is a market aberration and therefore to be minimised.
There simply isn’t anything at all in neoclassical economics which says that all government activity is a market aberration. Nor that it must be minimised. It’s simply not there at all.
Now, if you were to say neoliberal then perhaps you might be getting somewhere. But neoclassical economics is just a result of the marginalist revolution. Given that MMT accords with that basic idea, to look to the margins, it’s also neoclassical economics.
Note that he’s also trying to insist that Keynesianism is neoclassical, which it is, but then that it regards government activity as something to be minimised. That would be a hell of a surprise to Keynes.