It might not be about 'all birds' .. But it could be about THIS bird. For it to have enough force to break through a window, it would have to have been flying pretty fast and completely distracted .. Perhaps this happened during the course of a hunt or it could a neurological complication of some sort .. Who knows?
It might be an idea go contact your local Ministry of Wildlife or the equivalent .. And report the incident. I'm sure they would like to know about this bazarre event. They do study animal behaviours which helps to monitor disease and health issues.