How does he know Chrome is transmitting ALL conversations that it hears? His arguments aren't valid:

"(Ok, so how does it know to start listening just before I’m about to say ‘Ok, Google?’)"

This could easily be achieved offline.

The same argument could be made for Siri, a wiretapping device which you carry with you all the time. In fact wiretapping your phone would be much more effective then wiretapping a computer browser application.

Before making such accusations he should present some solid data, like network traffic from an idle chrome application during conversations (with and without saying "Okay Google"). If an idle chrome application was always transmitting data to google, he would have a solid argument.