I don't think there's any way to know for certain post-mortem; but at least in all the descriptions I've read of strokes, causing a sudden fall within a split-s

I don't think there's any way to know for certain post-mortem; but at least in all the descriptions I've read of strokes, causing a sudden fall within a split-second seems unusually abrupt, while falling is an extremely common and ordinary event in the elderly and having a stroke after hitting your head so hard as to break your nose doesn't seem like too surprising a thing.