Oh, Menley! I get this when abroad, too. Some lost soul will spot me as somebody LIKE HIM/HER, and feeling lonely and isolated will plop right down and start in -- and I have more than one potential compatriot source to worry about!) It feels desperate and grabby to me and makes me very uncomfortable.
How does one discourage the lonely and socially desperate when one is neither, and really, really, does not want to make a new buddy, go to the museum, take the bus tour, have a Bubble Tea, meet for dinner, go for karaoke, whatever? "I'm on a business trip so I have almost no time to myself. In fact, I have to get back now. Have a wonderful trip, though," is my usual response, said while disengaging. I am quite fine on my own in strange places and am not a particularly social person, but I can't help but feel very sorry for these people and never feel I have extricated myself quite gracefully enough!