Runway incursion episode/incident
From your description, you did nothing wrong. But, there is a possibility that one of you was on the wrong frequency. It is hard to prove that unless the radio calls were recorded. There is iPad software for recording your radio transmissions.
The more important lesson to be learned is that a nontowered  field is supposed to be pilot-controlled. But, it is perfectly legal to fly in pilot-controlled airspace without talking on the radio. Even if neither of you made a radio call, you would be within the FAA regulations.
The mistake that was made was that neither of you maintained situational awareness. You should always visually clear the traffic pattern while taxiing to and holding short of the runway. This is especially true for final approach. In the case of a high-wing aircraft, you will have to angle the nose of your aircraft downwind toward final. Otherwise, your wing will block your view of final.
P.S. It might not be a bad idea to file a NASA report.