(I honestly don't know and was thinking Matter and Thread were somehow related and the were both good and I hope someone can confirm or explain what I am missing.)
https://en.wikipedia.org/wiki/Thread_(network_protocol)
Matter is a network protocol which provides a standard API for how smart devices talk to home hubs. By making devices truly platform agnostic, it will end the dark "Best Viewed With Internet Explorer" direction which smart devices have been going down.
So I guess if you trust apple, you can sorta trust these devices as their access to the outside world would be through an apple device.
The Apple TV 4k 3rd gen and the new HomePods can be Matter hubs (both have Thread hardware).