Until watchOS 26 is out to the public, they will update it once it’s out with these features
That sounds reasonable, but the older watches are updated with the other things from WatchOS 26 like Sleep Score. I'm going to assume it's an error. It would make me pretty mad if they us beta testing a new feature that we can't actually have unless we buy a new watch, and then pretend it's a hardware limitation. Also seems unethical to hype up an OS with features where some of them are actually only going to be available with yet-to-be-released hardware.
But surely Apple wouldn't do that, it's gotta be a typo.