Let’s keep some things in mind here:
Korea is not the West. Love motels and whatnot notwithstanding, it is still a conservative country. The neighbors witnessed something out of the ordinary and called to complain about it. Regardless of whether we Westerners think that the host is in the right, she’s still on foreign turf and must comply with local laws and customs. To the neighbors, she looked like a promiscuous woman. This isn’t the truth, but it’s now things looked. A friend of mine ran into the same problem when she hosted parties for the soldiers in her town. She never so much as kissed any of them, but their staying overnight prompted her neighbors to complain to her school. Again, this is about customs. Couch surfing is indeed a fine idea and a good way to bring people together, but it can cause trouble in a country like Korea. Frankly, I wonder if she would have gotten a complaint if she’d hosted women instead them.
The lesson to be learned here is that foreigners WILL PROBABLY BE HELD TO A DIFFERENT STANDARD THAN THE NATIVES.