Short answer: Orinda is geographically the westernmost Lamorinda town and its BART station is one stop closer to San Francisco than Lafayette. Lafayette also has direct BART service. Moraga has no BART station, so its total trip includes travel to Lafayette or Orinda or another connection.
Local Context
The shortest rail segment does not always produce the shortest door-to-door commute. Distance from home to the station, parking, school drop-off, traffic, transfers, and the final San Francisco destination all matter.
What to Verify
Compare representative trips with BART’s official Orinda and Lafayette station information and current trip planner. Test the trip at the actual commute time.