DASH-8 TURBOPROP suddenly ROLLING BACKWARDS on the runway before DEPARTURE.

What happened here? Honestly I don` t know. Last tuesday I filmed this Air Berlin Dash-8 departing under Eurowings callsign to Nuremburg. It` s normal for the Dash-8 to put up the speedbrakes before the departure but I have never seen one of them rolling backwards before starting the takeoff run. I asked a student pilot and we had a suggestion but I am not sure if it` s possible. It was a very windy day and the speedbrakes above the wings probably functioned as a sail and pushed the Dash 8 backwards? Probably a Dash8 FO or Captain is watching this and can tell me if this is a reasonable suggestion.

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