Just because you don't understand its reasons doesn't make it a random occurance. I'm guessing you were near a nest or a fledgling, but that's just my non-educated guess.

Another possibility is that you looked like a former 'enemy' of crows. Crows can remember people who mess with them for up to two years and seem to be able to communicate that information among their peers. There is an excellent documentary about that behavior and it may have even been about scientists in the BC area.

They wore masks to test whether the information could be passed down from generation to generation. They found one crow offspring that still recognized the mask its parents had been trained on.

I believe it was called "The Intelligent World of Crows". It was excellent.