No, he is not the owner of Mastodon. No, his company is not responsible for what happens there, because there is no company or similar. A non-profit foundation (chaired by Eugen Rochko) develops the software and launches it on mastodon.social, and that foundation does not even participate in what the rest of the instances do. They could go crazy tomorrow, sell the domain or change the software to make it more invasive, the rest of the instances would be sent to hell and the network would continue as if nothing had happened