Comment by n4r9

My take (possible spoiler):

If he had no hats, then his statement would technically be true. Therefore he has at least one hat.

He may have some green hats and some non-green hats, but must have at least one non-green hat. He could have any number of green hats, including zero, as long as he has at least one non-green hat.

So the only derived statement that we can conclude to be true is A.