The everything is computer line is obvious just a excited utterance with Trump just forgetting an a.

I'll go a step further. It's, I believe, technically grammatically correct. If you're talking about a singular computer system or concept. It's not worth arguing semantics, and I don't know for sure, but it's not wrong like they want to act; everyone knows exactly what Trump meant, it just sounds a little funny.

I think "everything is computer" sounds better than "everything is a computer," personally. The former has more character, and instantly became a meme. It's got impact.