Yes! They should definitely try that experiment! When reading the article my first questions were: do these people think there is a real human at the other end

Yes! They should definitely try that experiment! When reading the article my first questions were: do these people think there is a real human at the other end, and, if so, do they think the photo is of that human? It's probably impossible to answer that question directly, but putting up a notice similar to "you are talking to a real person, not a bot" and seeing how that affects the behaviour would give some indication, perhaps.