I believe the lack of charges for lying to Congress does lend a little credibility to the story he tells.
The tobacco execs who testified to Congress that nicotine was harmless and non-addictive didn't get charges, either. Does that lend credibility to the claim that cigarettes are good for you?
Fuck no, it doesn't. Because nobody has ever been charged for lying to Congress. Even when they've been bald-faced directly lying to Congress.