If they publicly state that the house is a "town square" (he has said that of twitter), and they say that they are a "free speech absolutist" (he has said this of himself in the context of this house/town square/website), and state that "By 'free speech,' I simply mean that which matches the law.", then yes, if they don't let you spray-paint (tweet) whatever you want that's not strictly unlawful (like, ah, calling for civil disorder in the UK?), they are indeed a hypocrite.

When the house is digital (twitter is), why even use spray paint as the analogy?

Can't throw rotten tomatoes at internet nazis in the nazi "town square" unfortunately.