Do you have a right hand drive truck? That is the only way I can make sense of that picture...
LOL, I thought the same thing at first, then I saw the steering wheel and column at the bottom of the pic. It's taken from inside. Also there's the hanging pedal.
So the master cylinder is under the dash - real easy to get to.
There's no way you'll be able to look down into the reservoir from under the truck unless they lowered it.
Inspection mirror?