TBF tons of people have lung cancer and still smoke and live with smokers so I wouldn’t say him and Bridgey smoking is an indicator of whether or not they’re lying. It’s unwise of course and the doctor would tell you to quit but people do stupid tit all the time, that’s why outside every hospital there’s a cloud of smoke and people on home oxygen have to be begged not to smoke on it so they don’t blow themselves up.
The rest of the factors are way more indicators of lying about the cancer, eg the fight and that he’s still in what seems like full energy and fitness mode and the story makes zero sense.