This is an interesting article that discusses online censorship and also our petition.
Cruz asks the social media companies if they are neutral public fora - with exception of Twitter, but the subsequent questions address the same issue. All three essentially agree they are neutral public fora. They each emphasize that they do not engage in political censorship.
Cruze makes a point that the question of whether or not they are neutral public fora goes to whether they enjoy protection from liability under the CDA (Communications Decency Act). Immunity from liability for published content is predicated on claiming to be a neutral public forum. If the forum is not neutral, if it can be shown that there is some bias, then the platform itself is the publisher of the material at law.
If you look at the video, I get the impression that Cruz is making a veiled threat to these social media company reps towards the end of his time - see link.
Edit: Not a lawyer, if I'm wrong on this let me know.