Methinks someone lost his canopy when he wasn't expecting to ….
It might have helped if you have posted this on the PvP sub-forum, more likely to get a response there
Any hull damage regardless of angle can potentially damage the canopy, though direct hits are far more likely to. Or it could be super-penetrator rails.
Above, with almost anything, though only with a perfect shot or with explosive.
A lucky railgun hit can do it from any angle, if not blocked by another module, and penetrator rails will pass through nd hit all modules in their line of fire.
Do note that lag + latency compensation can lead to a very asynchronous experience, in some cases; in some PvP engagements, what you see may not be what your opponent sees...the game will still register hits on their terms.
Shots do actually have to hit the canopy, but there are a huge number of variables and many ways this can happen.