I didn’t doctor the copy/paste (except for redacting the MAC address)… Weird, now I’ve been nerdsniped.
EDIT: No, this makes sense… but is also worse: Network address is 1.2.3.4, usable IP range is 1.2.3.5, 1.2.3.6 and broadcast is 1.2.3.7… Which means they’re assigning the network address somehow. And I guess somehow the router/remote device just says “ok”… I’m leaving this alone lest I lose more of my sanity.

(Also there are lots of parallel subnets and, to the best of my knowledge, no firewall doing anything meaningful between them… shrugs)