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Strava uses the GPS data as last resort for the distance measurement. If you've got info from something equivalent to a GSC-10 (speed/cadence sensor) then it'll use that, even if it's woefully inaccurate or only partial data.
Stripping that stuff out of the file and reuploading will work; so that Strava will then default to the GPS trackpoints.
If it's a .fit file then convert it to .gpx (or .tcx). Then edit that and remove the DistanceMeters tags (there will be hundreds so it'll need a text editor that can do regex search/replace).
Feel free to email whatever you've got to me (alex @ <username> .org) and I can do it.
Distance on this is not, I believe, correct: https://www.strava.com/activities/534362056
How do I change the distance?