Oh Me Oh My,
Having been a LAME that used to physically carry out the refuelling at the aircraft fuel panel, I'm very aware that was our job and still sign off on it.
One man transits, at this stage ( and has been for some time) will be for domestics. That's still a sticking point on the international side of things.
You make an observation about two types of observation. Yes there is direct and yes there is supervision of the overall operation. You can have direct supervision and prevent something happening, or supervise something from a distance and see it go pear shaped. Either way you have supervised the operation.
The term supervision was/has been used very loosely on this thread.