Did you have a workshop? This is a common exploit griefers are utilizing. They form a party and then stalk the workshop owner, a player in the team will activate claim on the workshop and it will open you up to pvp no matter how far away from the workshop you are. They usually wait until you are completely defenseless to one shot you in the back.

I've seen a lot of stories like this recently since the most recent update. I assume it's because of the huge unban wave that happened. Some those that were banned had to sit and destroy a lot of their inventory to continue playing, causing them to accumulate salt and have therefore resorted to taking their frustration out on other players.