Mac Pro showing on network

[needforspeed]

Hi, my relative was complaining that there is an unknown Mac Pro showing on their iMac under Network heading? At the time my relative had their Mac Pro connected to their iMac. The Mac Pro has the name of the relative.
I'm not familiar with Mac OS. I have checked the DHCP leases on the router. Their iMac and Mac Pro are connected via wireless.

I have posted before about my relative borrowing my USB flash drive and the anti virus on my computer detecting viruses on the USB after.

 

[needforspeed]

There was two Mac Pros connected to the iMac. One of them is the name of my relative and the other is like Mac Pro xxxx the x are numbers. Why was there two Mac Pros showing on the iMac?