If it was a server reset, I think the admins would've told us by now. Probably some equipment failure or a hacker attack, your guess is as good as mine.
My character rolled back, in regard to location and inventory, as well as my base no longer existing with the exception of a sleeping bag and a chest I'd laid down near one of the farms (one without the Fuel Tank). The chest still had the items I'd place in it (some wood items left over from my beginning to build). The point to which it seemed to reset was about 24 hours before the time I'd last played. As for the cause, I haven't the foggiest, though I'd say that a legit reset should have removed my chest and sleeping bag. Curious, no?