This is a random encounter, the map is usually empty. I have also had a similar thing happen in this map, it is one of the maps that can get such encounters.
As you have experienced, this is also a map that you need to travel through the middle of, right where the hostiles are, unfortunately.
Your options are basically to either stealth past these guys, or wait until you are powerful enough to take them out. I had the same problem. Good luck!
