But I'll take the flattery. :)
My favorite language story is from when I was studying in eastern France (Strasbourg). I went across the border to the train station in Kehl, Germany, as I reasoned that train tickets inside Germany (I was on my way to Berlin) would be vastly cheaper than trying to buy the same ticket with an origin in Strasbourg.
Anyway, I know a little bit of German, and suddenly I understood why foreign language classes always start you off with directions and tickets and timetables and so on. So I was all set with my basic train vocabulary. We went back and forth and conducted our business. I gave him my American passport at the end, he seamlessly transitioned to some pleasantry in English as we concluded, and I walked away with my train ticket.
Well, as I walked away, I was pondering his lack of surprise that I was American (which should not have been surprising; my crappy German is clearly not a Frenchman's crappy German), and I replayed the conversation in my head. As I got to the "smoking or non-smoking" part, I realized I could not recall the German word (rauchen, for those keeping score at home). Eventually it came to me, and I realized that he had actually said "smoking oder non" (oder being German for "or").. Well, of course, English with a German accent sounds like German to an English speaker...
And I suddenly realized that we had probably conducted virtually all of the transaction in English, and I had no clue. He probably switched to German-accented English as soon as I did a poor job of asking for a 2nd class ticket to Berlin arriving at this time on that date, and I didn't even realize it.
On the same trip, I was on a train from Italy to France. In my car was a French woman living in England, and an Italian woman. They were practicing on each other so the Italian would talk to the French woman in French, and she'd reply in Italian. This went on for some time. As we prepared to depart the train, the woman's child and husband joined her. I talked to the French woman's husband for 5 minutes or so. Eventually he asked me where I lived and I told him I was from California but studying in France. He turned out to be British, and switched to English and said "oh, well then I guess we can just speak in English then."
I'm sure our French pronunciation wouldn't have fooled a native, but it was good enough for a couple of foreigners.
One time when I was about 16 or 17 I was sent to do an installation at a dairy farm; specifically in the small trailer near the barns where a couple of Mexican migrant workers lived (the farm owner being nice enough to get them a TV subscription, I guess). In this area of the country there aren't a whole lot of Spanish speakers, so I'm guessing that the guys who were hanging out in the trailer just assumed the goofy looking white kid would have no clue what they were saying if they spoke in Spanish.
Little did they know that I studied Spanish in school for the better part of a decade (and actually paid attention/practiced), so I could understand most of what they were saying, and it was not good. It was a lot of complaining about the farm owner (who did not speak Spanish) and about how this "trash was not an excuse for better pay and working conditions". They definitely sounded bitter about their situation.
So when the time came to activate the satellite receiver I had to use their telephone to call the provider to turn it on, for fun I asked, "Puedo usar el telephono?" I have never seen anyone get more quiet and solemn this quickly. Neither of them said another word the rest of the time I was there, presumably in fear of me ratting them out (of course I didn't).
Here in Canada we have a french region, and if you walk into a mechanic's shop and say: “Hi! Does anybody speak english here? Can you fix my car?” They will help you, but if you make an attempt like: “Bon Jur. Can you fixé le car for moi?” They will be a lot more happy to accommodate you in English because you tried to bridge the gap. Maybe it's similar!
Have you considered the fact that they might have been foreign tourists like you? A French hiker would not greet you in English unless he clearly heard you speak in it on the way in, and even then. (am French).