I heard it suffered a knockdown from a strong gust of wind. But that sort of ship shouldn't sink from a simple knockdown.

The ship should be entirely self-righting after a knockdown. Ideally the lee side ports would be closed so the ship doesn't take on water. But even if open it takes a whole lot of water to sink her. Which suggests that they didn't close them after the knockdown and may have abandoned ship before any damage control, close the ports and start the pumps, was attempted. The majority of the people being students, with little or no sailing experience, would have only added to the confusion and panic.

Of course if the ports were left open for several minutes and no other corrective actions were taken sinking is the inevitable outcome. Sailing ships are remarkably tolerant and forgiving but there are limits.

Seems to me there is something odd about how it all happened.