You'd have to be a real heel to rob a good samaritan.
Call me cynical, but I would have suspected a setup. I would have helped, but kept my eyes on the bike the entire time. There are a lot of distract/steal scams going.
Ironically, much of my cynicism comes from having lived in Oakland.
Example:
Once, in San Francisco, I gave a few bucks to a guy who said he needed bus fare back to San Jose. A week later I saw the same guy, in the same area, running the same scam.