It was polite of you to tolerate the old man's story. Correcting him would have done no good, as he would have probably been offended while still thinking that he was right.
I have a hard time keeping a straight face and a shut mouth when dealing with these people. Guys with no classic car at all, calling every 340 or 440 a six pack, bragging about their POSI axle, etc.
Yup I agree, even when I know I'm right and someone's wrong I just listen and laugh in my head. Sometimes when the person actually hears what they are saying maybe later they can understand they were incorrect.