Had a strange scraping sound coming from the front right wheel while driving. Pulled the brake caliper half off to check the pads and the inside pad is worn down to smooth metal but the outside pad doesn't look to have been touched at all. Is this normal or a sign of something else.
This is a common problem, but it shouldn't be considered normal.
When replacing brake pads and discs, there are two things that are sometimes overlooked.
Lubricating the slide pins
The slide pins should be removed, cleaned, and fresh grease applied. The grease must be heat resistant and safe for use with rubber, for example ceramic brake grease or silicone paste should be used. If the slide pins are scored or corroded they should be replaced, similarly if the rubber boots are damaged, replace them.
Some brake pads will come with new brake hardware, this might include stainless steel shims that sit between the pad and caliper bracket. These should be replaced with each brake pad replacement. The point where the shim makes contact with the caliper should be coated with copper anti-seize or similar. This prevents corossion between the two surfaces, which can cause the shim to raise up slightly and clamp down on the pad, this can stop the pad from sliding freely. Any corrosion should be removed with a wire brush. Any other retaining springs or pins should also be replaced.
You should replace both sets of pads with fitting kit if there is one and follow the above advice, the pads will wear evenly.
It is a sign that the calliper is (partially) seized and not moving properly - leading to uneven wear : they need servicing... It is unlikely that the material was softer on one side - unless someone made an error fitting the last set of pads. One reason pads should be changed as axle sets...