The softener tank collapsed because of the vacuum.
Not sure why the pump would have reversed itself, but it was pumping the air out of your pipes back into the well (or cistern or ?). Also, not sure which pump you have. There is probably a valve or flap that opens to draw water in from the well (and closes to keep from drawing water from the house) and closes when you push the water out thru the house pipes (and the house side is open). The flap or valve was out of position when you started the pump and so was closed when it should have been opened and open when it should have been closed. Priming the pump probably fixed it.