Pari’s story: interpreting politeness

I was standing in the metro. Some guys were standing next to me ( They didn’t understand german, just arabic, so I assume they were from an arabic country, although this isn’t a matter of nationality) and were chatting, they seemed to be in their 20s. I want to add that I directly came from school and I was dressed very modestly. When the train stopped at the station, they guy next to me let me leave the train first . I liked this act of politeness very much, that’s why thanked him and smiled to him very nicely. It wasn’t meant as flirtation or anything, I just wanted to be polite. But when I left, I heard them laughing : oooooooooooh Dankeschön Dankeschön ( which is the german word for thank you, that i used). They said it in a weird tone , then they started to say something in arabic. Of course I don’t really know what they said, but I am sure that they thought that the fact I thanked him in a friendly way, was a sign that I liked him. They continued grinning into my direction and that really upset me.
Generally, I have experienced that guys from the middleeast sometimes misinterpret politeness from girls. I am from Iran, and Iranians also behave this way. Another time, I was in the metro with my friend when a Iranian guy started talking to me, in the middle of our conversation! I replied politely but reluctantly. still, when my friend left the train, he talked to me all they way, asking how old i was and if i would give him my phone number . he was actually pretty nice, but it was still a bit awkward for me.
When I am in Iran, I experienced that if you look into a guys eyes for a few seconds or smile at him, he thinks you are interested in him. That really sucks. so – guys ! even if I am polite to you – it doesn’t mean I want to date you our stuff okay?