Inaccurate Fastest 5K and 10K Records in Apple Fitness App - How to Fix?

Apple Fitness awards don’t only come from intentionally logged workouts. They can be triggered by:

• Imported workouts from other apps (Strava, Nike Run Club, etc.).
• Old data synced from a previous device, especially after restoring from backup.
• Manually entered

You are someone who has access to your device and may have entered data, Kcal, or Distance manually. See the pic below, which is self-explanatory.

User data entered is explicitly mentioned, which can be seen on the 8th Screenshot.

This also may help you understand

For you to see the time in the Workout: change start and end time while manually entering the data

See the pic below