Why are there brown spots on my walls?

It certainly doesn’t look like mould to me, and it wipes off much more easily than other bathroom mould I’ve encountered. It looks just like dried splashes of liquid - you can even see the shape of the droplets where they have run down the door. I just don’t know why they’re brown!

BTW - I would doubt that it’s related to condensation, as surely any coloured impurities in the water would be left behind when the water evaporated. So I think it must be either liquid water splashes, or, if it is to do with condensation, it’s something in the wall/door/ceiling that is leaching out when water condenses on it.