Distance covered by mules and donkeys counts towards distance covered by horses.

Steps to reproduce:

1. Spawn a mule and/or donkey
2. Put a saddle on the mule and/or donkey
3. Ride the mule and/or donkey and walk forwards

Observed Result:
In the escape menu -> statistic -> general tab, scroll down to "Distance Covered by Horse". It increases.

Expected Result:
The "Distance Covered by Horse" statistic should NOT increase since you haven't rode a horse.