I thought the same thing, but I double checked the units used, and I can switch it to kilometres, which switches the distance to ~2.6 kilometres. So, unless something with the scaling is wrong throughout, I still think that I must have done something wrong.
For the time being, I have switched the label to say "Kilometres", which is accurate enough for what we are using the map for.
I will still investigate what is causing this problem, because it is incredibly frustrating!