I did some more digging on this and figured out the foreign IP belonged to LogMeIn Hamachi, which I had installed for testing purposes. I didn't expect that it would show up as a choice when I looked at the local host list when connecting to FM Server.
Sorry for the wasted bandwidth.
It is always fun the way we manage IP's the way we do with DHCP, NAT (and double NAT), port forwarding and sharing a LAN and WAN IP at the same time and other workarounds that we have done to maximize IPv4. It will be nice when we can all just have one simple IPv6 address that is unique and works everywhere. I'm sure IPv6 will have some challenges too, but at least it is a lot more secure and unique.
I will note for those of you new to IPs and network managing, FileMaker performs much faster connecting to LAN clients via a LAN IP (e.g., IP's starting 192, 172, 10, etc.) and not a WAN IP. So, if you give your FileMaker Server a WAN (public) IP, then you could really be slowing down your LAN clients without realizing it. That is why it is REALLY nice to have multiple ethernet ports like on the Mac Pro, the old xServes, and most Windows Servers. You can assign a LAN IP to one ethernet and then plug a second ethernet in and give it a WAN (public) IP. Too bad Mac Mini's don't have a 2nd ethernet, and neither do most other Macs. It is a very useful feature for a server.
I've gone into quite a few clients places and made this change and had them all excited about how much faster their FileMaker server now runs. I chuckle, because nothing changed on FileMaker, it was just a matter of properly configuring the server and its network connections. It is interesting how little many people know about how their TCP/IP network works.