The perception that female photos look fake is still sexism. It suggests people believe it less likely that a woman would be on the other end of the conversation. And you suggesting that perception as an explanation without challenging it kind of demonstrates how this is a pervasive problem.

Now I agree that the model photo looks a little more artificial for reasons beyond gender, and they should probably have compared with a male model photo as well. Though personally I suspect people would still think it more likely that an attractive man was a real person than an attractive woman.