gps-speedsurfing

I recorded a top speed of over 50 kts on my watch today, on foil. Clearly not correct, and no, not while in my car driving back. I uploaded the track - everything seems normal and my averages are where they normally are. Except the top speed, which places me above Pierre Mortefon and others in the ranking. Glory for a moment. I deleted the track, it is clearly not correct. But what could have caused such a blip?

DSC