Jeremy either did smuggle heroin. Which shows he had a lot of courage, was stupid and greedy.
Or he did not smuggle heroin but boasted to people he had. Which means he lied and wanted to give himself more gravitas. It also backs up Julies claim that Jeremy liked to say things that would shock people.
Or Claire Powell's book made up the claim. But as Lookout said she interviewed everyone, including Jeremy. So no need to make anything up.