How can I confirm if my ISP is leaking private IP addresses outbound?

Doing some tinkering around the local network I found a device with IP 192.168.49.1, happens to be a Canon printer (still figuring out how this happened, but that's another story).

Ran a ping tool and the traceroute takes it 6 hops beyond my network, two ASs away.

Is this normal?

pastebin here: https://0x0.st/zAlM.txt