If I recall correctly, that ruling came down from an ALPA question about those very questions. I was werking for a small company contracted as a US Air Express carrier. We operated under both 135 and 121 at the time. The 135 pilots were arguing that same question(it was duty time if you were on call). The 121 side of the operation had no problems with that interpretation.
It went to ALPA legal, then to the FAA. That was the interpretation they sent to the company, and everything was fine from there on out. Just to be on the safe side the company converted all operations to operate under the 121 rules.