I’d say that the de plays here the role of an indefinite article. Without it, the boy would be referring to the TV in the living room, but he wants to refer to the act of watching TV, so a much more indefinite TV.

It may be easier to understand by rephrasing:

Faire de la Playstation c’est pas comme de la télé.

Here, de la télé must be understood as regarder la télé, and without the de, you’d be referring to the television as an object, not as an action.

Explanation is even simpler :

There’s a négation :"ce n’est pas". After a négation you must have a defined article (le, la, les), an undefined article (un, une, des), or "de" which means that the word that is unquantified.

Compare to English :

That is not a car
Those are not the cars
That is not water -> no article in english -> that’s where you use "de" in French (expressing an unquantified amount) : ce n’est pas de l’eau.