This is interesting!
However, can't it switch the unit to meters, not miles?
From the link you provided, it appears the API doesn't include information about its unit in the responses.
So, it's confusing.
Edit: I've had my coffee now, and see what you mean. the API exposes it at /api/systems/{system}/lines/{line}, as well as aggregate for the system at /api/systems/{system}, working on supplying distance unit in api response now.