What 8.1 screen is it appearing on? It isn't just an entry in File Explorer under the Network Heading is it?
Your screenprint shows an unknown device in the table on the broadband setup page. Can you account for that entry? Not sure whether you were indicating that it did or it didn't relate to the Sony entry.
Windows may have tried to install some phone, or even some other device, at some point in the past via upnp and just be showing you what it identified as a network device.
never trust a man in a blue trench coat, never drive a car when you're dead
All the router entries are valid. The 'unknown' is my phone. Sometimes it shows up as unknown, somtimes as kosPhone. My network setup is /awful/ and leads to some annoying problems like that.
Good idea! I'll do that now. Only issue is that I have a Sky broadband booster thing, and anything connected to that is presented to the router under the booster's MAC address (which is /really/ annoying, as I want to reserve an IP for my rasperby pi but it connects via the booster (as it's about 6 inches away from it) so I can't :@ )
Then you're probably fine. (So long as it's decent software with updated definitions.)
p.s. Most people have this condition called "sleeping" - it's a rather annoying occurrence, but it does at least provide a useful period during which non-interactive tasks that take many hours can be scheduled.