Unknown Netgear IP address on network (CG3000V2)

Sorry, the telnet details don't give me any clues, although it does confirm that there is a device at that address. Try switching everything off except the router and the device you're running fing on, and then rescan - if it disappears, turn the devices on one by one, rescanning in between and see if you can locate it that way. If you still get a response after switching everything off, unplug all the LAN cables from the router & rescan, if it is still there, change the encryption keys & rescan.