RSD sensor is, as you surely know, monitoring network traffic on the machine it is installed (which can be an everyday computer or a DHCP server in which case monitoring is somewhat different), by looking into network packets and gathering info from there. In the case of a DHCP it monitors DHCP requests, too.
As for the unusual IP, I suppose that could come from a manipulated network packet, sent by something on that computer. Or just the IP could not be revealed fully.
You did not write where you have installed your RSD sensor and how many there are and if the same LAN or in the WAN, or on the DHCP.
I'm not a network expert at all, but could n ot you find the trace of the computer that you mention by its MAC address (supposing that's not spoofed) in either of the many network device you have ?
Also: could you detail the "ping" that you refer to here? What so you mean exactly by that? What is that ePO "can ping" the computer?