On Saturday, July 21, 2018 at 2:15:40 AM UTC-7, wrote:
I would have interpreted the mention of 48 knots as being a descent rate shown on the data recorder file (= around 880ft/11seconds).

The report clearly says airspeed not descent rate. Default Flarm setting is 4 second fixes so 11 seconds represents at most 3 fixes. 11 seconds from normal flight to impact indicates a very low altitude no matter how you interpret it.