I've lied about my birthday while signing up for websites before. I've also made ad-hoc email addresses with forwarding to conceal my main email address. I've given fictitious phone numbers and I've used the names of fictional characters. I do this because I benefit from the service but I don't trust the provider to use my information responsibly.
Not a logical leap to go from there to feeding fake data to extensions when they request data that the user deems unnecessary for their functionality.