What it looks like to me is that a stick entered your front wheel below the fender support. As the wheel turned, the stick caught the fender support forcing to upward towards the fork crown and pulling the fender with it. As the fender flexed, it cracked in half and the bottom half with the mud guard continuing to be brought to the fork and the top half of the fender popping back to relieve the stress. The stick may have been broken either by impacting the fork and being driven by the spokes or by the primary impact with the fender support. In any event, the fender mounting assembly slid into the front brake displacing it and likely the displaced brakes seized against the rim tire causing the crash. At least that would be my theory.
Glad you escaped without significant injury. Hope you heal quickly and can back to riding soon.