Advice on Changing Pads in a Parking lot

If the passenger side wore out that soon, I bet the pull was to the right.
As already mentioned; there are three possibilities;
1) the right side was dragging continuously causing the pull and frying itself.,Or
2) the left side wasn't working at all, and so the right side had to do all the work, Or
3) some combination of the two.
As to #1) On KH 4-piston calipers there are only two things that cause this situation; either the pistons are seized or you have a problem in the line,be it a plugged hardline or a collapsed hose; some already mentioned.
As to #2) This can only point to seized pistons, or a bad brake line, either hard or flex.

So I would look at the left side first to see if it's working. This should be an easy test. Just spin the wheel and hit the pedal hard and fast, then immediately release. You will need a helper on the pedal. The wheel should slam to a halt, and then you should be able to freewheel it as soon as the brake is released, as in, instantly. If it does not instantly freewheel, something is wrong! If it does not apply, something is wrong! It could be hydraulic, or it could be mechanical. We will have to find out which.
The next thing I would do is crack the bleeder and have the helper gently apply a little pedal and see if the fluid comes out in a nice steady stream. If it doesn't, the line is plugged. Go up to the Combination Valve, and crack the line there,looking for fluid. If you get it there, go down to the flex line and check the m/c side. If you get fluid there, replace the flex line.
But, if fluid came out the bleeder, then the caliper is bad, or 1 or more pistons is stuck. To find out what's going on, you will have to pull 1 pad out. Then watch the pistons as the helper gently depresses the pedal. Do not full stroke the pedal, there is no need for that. As soon as you see 1 piston begin to move, signal the helper to stop and release. The piston should immediately retract a few thousands of an inch. Repeat as often as necessary until you see it retract. As soon as that piston is proved, install a spacer in there to prevent that piston from moving. (Perhaps you can flip the pad back in there standing on its end.) Then prove the second piston is similarly retracting. When that side is proven, lever the pistons back into their bores and re-install the pad, then pump the pedal a couple of times to normalize everything. Now remove the other pad and check those pistons similarly.
The seal-retraction is usually pretty small, but the KHers have pretty fat square section O-rings that when new,pull back more than most. I'm gonna guess at least .005 to .010. The O-rings last forever, but the grooves rust up and then the retraction becomes less. But, the thing about KHers is that the pistons fit really tightly in the bores, and it doesn't take much rust to cause them to seize up. So go find the seized piston(s).
But I don't think you will have this problem. More likely is a problem in the flex-hose.
And if this side is working 100%,then,we're off to the otherside,lol