Are you polite when someone says something to you that makes them sound stupid and or gullible?

I recently had a conversation with one my father’s business partners at his place of work,he started talking about a guy who had just walked in through the door.
Will,the recently hired forklift operator.
He was eagered to tell me this new guy’s interesting life story.
It turns out;Will’s entire family was involved in the manufacturing of crystal-meth among many other illegal activities,,,,,Will testified against his entire family which was very instrumental in their conviction.
The police and DEA were very thankful to Will for his assistance and they knew he would be in severe danger for cooperating therefore to protect him *“They put him in the safest place they could find ,,,,“IN JAIL” and kept him there for 3 months!!
{*WTF,I heard in jail you can have someone shanked for a pack of cigarettes }
I don’t know how but I was able to keep a straight face but should I have told my father’s business partner that he was a gullible idiot?
Should I tell my father that his business partner is an moron ?