Yes necessarily, while it is true that a master cyl that is failing can cause that light to illuminate you will notice increased pedal travel and reduced stopping performance before that occurs. It will also be seen as uneven wear from side to side, IE the LF and RR or RF and LR pads will wear quicker, thanks to the diagonal split braking system. Seen it waaaay to many times. A leak could also be to blame for certain, however that will rapidly progress to a light that is always on and a low brake pedal.
However the OP's listed symptoms are consistent with a pattern I've seen over and over again. Which is the pads are worn to the point that caused the fluid level to drop to the point where it activates the light when stopping or on steep hills.
Recommending the addition of fluid is just irresponsible. The fluid level went down for a reason, so that reason should be investigated. The vast majority of the time it is just due to pads that need replacement, but if it isn't there could be bigger problems later as it progresses.
In normal operation there should be no need to add brake fluid. The cap should never even come off the reservoir. It is one of the many reasons I hate Monkey Lube places. Way to often they add brake fluid as a "courtesy" to their customers when in fact they are doing them a disservice by defeating the low pad warning built into the Ford system. Ford has been doing it that way for a long long time doing away with the tell-tale scrapers and avoiding a pad mounted sensor.