There are many issues with your assumptions, settings, and procedures. I'll point a couple out:
- 100C is a very low oven temperature...not a problem, but it will lengthen the cooking time.
- Ovens are notoriously inaccurate. The temperate inside your oven was likely not 100C and could have been much lower (or even higher), but you didn't measure it, so you don't know.
- A potato is fully baked when it reaches about 100C at the core. So, with your oven set at that temperature, I would guess it would take several hours to get the internal temperature of a potato to that point.
- If your reporting of the internal temperature is accurate, you baked it perfectly, so it would not burn or caramelize.
- Potatoes are quite moist, and evaporative cooling keeps the surface temperature well below your oven temperature, not a situation where caramelization would happen.
- Paper will not ignite until somewhere in the 225C and above range, but that varies depending on thickness and moisture content.
Given all of this, your results are not surprising. It would probably take a few hours to bake a potato in a 100 C oven. Now that you know a potato is "baked" when the internal temperature is about 100C, you can save yourself some time by setting your oven at a higher temperature.