Not plastic, it's made from Sand
ETA of course next week they will find something wrong with it too small

Pardon my paranoia. Teflon was once considered a safe alternative also. As was magnalite (magnesium cookware), aluminum cookware, et al.
We keep advancing and that is a good thing.
Yes, I prefer cast iron after scraping the teflon off the aluminum pots.
Plastic is defined as organic polymers. Since silicone is a silicon based polymer -(R-Si-O)-, you are correct, it is not considered a plastic. It can contain carbon in the R- groups.
Word for the day: polysiloxanes