Keon opened his mouth as he wants to say something but he just closes it again after a few seconds. He wants to refute but he also doesn't know what to say
Craige's words are all true. Lie detection abilities aren't omnipotent as lies are pretty subjective. If a person believes that fire is cold then even if his statement is wrong, as long as he believes that fire is really cold, that wouldn't be a lie
Besides that, Keon also realizes the implication of Craige's words. It was not a threat but it was close enough. In the end, whether Keon's statement will be accepted and trusted depends on what the higher-ups want to believe
There are tons of ways to twist a person's words. Keon's earlier confidence was completely crushed by Craige easily. A smart opponent is indeed a terrifying one. You wouldn't know how you would be attacked