Yes, since workers run on whatever datacenter receives the request (which is determined by the DNS zone/hostname a client connects to), the datacenters that run your Worker code are whatever datacenter the client hits. This applies to your whole zone and not just Workers/KV.
The reasoning behind this behavior is due to two things - peering and network prioritization. Network prioritization means that, depending on how loaded/overloaded certain datacenters are, websites on lower-tier plans will be routed to different datacenters that have more capacity. For more on this, read this explanation.
To add a little more insight, KV is different from workers in that your data isn’t really pushed and stored to all Datacenters, rather it’s centrally stored and only cached at a datacenter if it’s frequently read:
Workers KV read performance is determined by the amount of read-volume a given key receives. Maximum performance for a key is not reached unless that key is being read at least a couple times per minute in any given data center.
Interestingly, I’m getting very varied results on my Cloudflare Workers account (Paid). Out of 4 domains, 2 of them are going to the colo that would equal Business Plan according to your test-page. But two of them are going to free plan. This is consistent when testing from multiple locations. Very odd.
The only thing I can think of is the amount of traffic, 2 domains have a lot of traffic and 2 has very little.
That said though, the ping-time to the colo on free plan is actually faster than that colo which is closer.