I think this doesn't make sense.
Is there actually a realistic mechanism that makes this possible, or is there a gap in my hardware knowledge?
The IP is currently assigned to some router in a nearby carrier network that has decent connectivity to everything. Potentially the mobile carrier.
The OP happens to be connected to wifi at the DC. Tests across the mobile carrier network didnt take place thanks to route preference over wifi.
Something in carrier land is responding to the IP. It might be assigned in a stupid fashion, like every PE router is responding to it. Or anycast or something.
The OP has the ip address assigned to his laptop and phone. His own devices are responding to the pings.
OP might be using a different ping client that he isnt used to, and is taking 40ms as .4 ms. He doesn't really give us the measurement, just the value.
OP might be using a VPN and the VPN gateway router is responding to this ip with pings for whatever reason. Or the VPN client software has assigned this ip to his laptop.
The same IP block is announced from multiple geographic locations, and so IP traffic will be routed to the nearest.
For example, go to https://lg.he.net choose BGP Summary IPv4 and plug in a well-known anycast address like 8.8.8.8 (operated by Google) or 1.1.1.1 (operated by cloudflare) and try a few different routers in different parts of the world, and you will see lots of different neighbors claim to be directly connected to these addresses -- something that should be very strange if you thought (for example) that an IP address had a geographic location at a particular point-in-time.
You can also try this for some of the addresses in this range and see that some of the addresses are like this.
I think more likely got something wrong with the units; System.Net.Networkinformation.ping reports in whole seconds (so this is ~400ms) for example. Maybe it is some weird tool or typo.