I'd urge anyone mocking him to define "consciousness".
It might sound silly that he feels his chat bot possesses it, but it feels no less silly to me than saying "Man believes chatbot possesses a Woozle."
It may, or may not, for nobody has yet said what a Woozle is.
The difference with Woozle is that people don't have an (vague, but still existing) idea of what consciousness is, or direct lived experience of it, that they can tap into for recognizing it in others.