I noticed something similar at university, coming from a tiny rural town - our otherwise perfectly lovely Muslim flatmates simply didn't want to be friends with us. I was so dim that I kept trying and asking them to join us when we went shopping or to explore London - every time a polite no, and they just hung out with other Muslims in a huge gang.
We also had about 5 knocks on the door in the first week - "are there any Muslims in your flat, we want to start a Muslim reading group/running group/lunch club etc".
Eventually a flatmate who was from London and used to it from school said to me, "dude, they don't want to be your friend!"
Meanwhile it was crystal clear why - their parents would ring them several times a day (and we had no mobiles then, so we all heard it!), asking what they were doing, who they were with, what they were wearing, trying to make sure they were staying in and behaving at all times. They had to be back in the flat for goodnight phone calls to show they weren't out clubbing. One of the fathers of one of the girls in our flat even wrote to the university to ask if his daughter could be moved to an all-Muslim flat (the answer was no). The parental pressure was unreal 
I thought it was such a shame - it made those girls miserable when they were 18 and had London in front of them to explore but their parents were still being so strict. Why let them see all that freedom but still try to control it so fiercely? Why drill into your children that they can only have friends who are like them?
However now I'm old I have a lot of Muslim friends from all different parts of the UK, none of whom behave like that with their children!