That implies your mudguard is not good for the person behind so just to the side means your not in the direct spray of the wheel. They are typically like this but a little additional mudflap fixes it normally.
Do you begrudge them getting home and out of the wet quicker?
That'd make sense for his position as I have 3/4 length mudguards. I don't mind people tailing (too much...) when they are cycling a similar pace, but he was going at half the speed before I caught him.