I have had two similar experiences. In one case, some bozo used the unpaved dirt shoulder to pass me on Sunset Bl. in the Brentwood district of west Los Angeles, along the frontage of Paul Revere Junior High (coincidentally, one of my alma maters). In the second case, I stopped for a red light in the middle of the right lane on a 4-lane road, to permit right-turners to proceed (legally) against the red light. When the light turned green, a motorist passed me on the right in the intersection.

Vehicular cycling is great, but it requires vehicular motorists!