It’s not uncommon to get trophies for a route you don’t own if the trophies are linked to a particular loco that is also used in another route that you do have. It’s happened a few times to me on other routes.
That happened to me with the DB BR 422. (I used the Haupstrecke Rhein-Ruhr version and I got the trophy “RRO: Lightweight Speeds: Drive the DB BR 422 at a speed of 70km/h.” (I think that’s what it says!) I don’t have Rhein Ruhr-Osten but I got it for some reason!
I also got that on the Xbox. The reason on why It unlocked it has to do with Sand Patch Grade GP38-2 getting the 10 miles. Also applies to Oakville Gp38-2 & Caltrain UP GP38-2. Same thing for Sherman Hill SD40-2 by playing sand patch grade