To answer the question, the difference arises from the measurement methods.
You are likely using a speed sensor, and that will report as the source. It’s the simple number of revolutions times the circumference you have set in TR.
Your friend has a similar deal, as his smart trainer reports speed based on his rear axle revolutions times the circumference entered in the trainer and/or TR app.
The difference between the two, assuming he is using ERG, may come from the fact that he can do the workout and hit the power targets at a range of gearing selections.
Erg allows you to use high, middle or low gearing. As such the “ride distance” may vary from one setting to the next, even on his, let alone compared to yours.
Does that make sense?