I don't know if Trump has complete control of the social media companies, though I'm pretty comfortable with the treason part. Legally, it's not censorship if a private individual or company does it -- it's just editorial oversight. Whether President Trump can arm-twist the social media folks (as previous presidents have done in other industries, without the color of law), I don't know.
But it doesn't make sense that Trump is just putting up with it, and it certainly won't make sense if this private "censorship" continues through the 2020 elections.
They are private companies but pretending that they are not censoring politically. They also push the Dem party candidates while pretending they don’t. So from what I read they are illegally being more or less political supporting orgs pretending they aren’t.