Hi Power of Two. I live in Calgary. My family may be unusual but we throw our windows and doors open, all the time. We just like fresh air, we live on a safe street, we are not worried about crime, we don't have AC.
All that said though, we never notice anything happening on our street. I once woke up one morning and left the house and found that the street had been dug up overnight by city crews; I hadn't heard a thing. I think folks can be wrapped up in their own lives and may not notice the sounds going on around them. It doesn't surprise me that no one on the L's street heard anything. I'm not familiar with the sound of gunshots, but I think it's possible shots could be fired inside a home and not noticed by neighbours inside their home. Plus the L's street is close to Macleod trail and a lot of traffic, so even if someone heard something, it's possible they could attribute it to traffic or a car backfiring. We are Canadian, we don't automatically assume a loud bang in the night is a gunshot, IMO.