I suppose it depends on how your website determines the IP address origin. They all belong to Cloudflare, which some services will report them as US addresses, regardless of their geolocation.
If you comb through the list at cloudflare.com/ips, you’ll see they come from all over.
Regardless, you really don’t have control over Workers origin unless you use Enterprise Plan’s Regional Services. Even then, that service really only applies to where your data is stored and processed.
Your only option would be to limit access to your website to all Cloudflare IP addresses, then use Cloudflare’s Firewall Rules to block traffic from the US.