The next assignment will be run through ChatGPT as well, with presumably the same results - resulting in failure and escalation to the academic dishonesty office.
Hanlon's razor "Never attribute to malice that which is adequately explained by stupidity" applies. This is an ignorant professor, not a dishonest one?
It can be both stupidity and dishonesty. To me, this reads like him doing something dumb initially, and then digging his heels in to avoid looking stupid or weak.