BMW take the cap off .overheated

What is your question?

I got my new car and in the same week i took it in for a service,2 weeks later i was coming home it was a hot day so i had the air on i live in the mountains outside of Bakersfield, well when i got to town my light came on saying to pull over and call BMW , i turned the car off and after about 10 min started it up and went home. well that Monday i took it to a local shop who i trust and he could not find anything but the cap to the filler not clicked like it says to do right there on it.It has been two weeks and i have had no trouble with it so far and even drove it to Las Vegas with air on no problem.i am puzzled.When i took it in for service did they not put the cap back on right do they check the fluid in there on a service they said they checked all fluids ???