Lying about anything at all to an immigration official is enough to grant you a lifetime ban to the US. I guess they took his message as lying about intent of visit in his application which they could label as "fraud".
Edit: Added source. All that is needed is that they believe you lied to a U.S. government official and they can ban you for life.
It can basically be considered fraud if this is true:
> When making the false representation, the person intended to deceive a U.S. government official authorized to act upon the request (generally an immigration or consular officer).
And this is the consequence:
> The person will be barred from admission for the rest of his or her life unless the person qualifies for and is granted a waiver.
Edit: Added source. All that is needed is that they believe you lied to a U.S. government official and they can ban you for life.
It can basically be considered fraud if this is true:
> When making the false representation, the person intended to deceive a U.S. government official authorized to act upon the request (generally an immigration or consular officer).
And this is the consequence:
> The person will be barred from admission for the rest of his or her life unless the person qualifies for and is granted a waiver.
https://www.uscis.gov/policy-manual/volume-8-part-j-chapter-...