So basically, you think everyone should always follow the more machmir shitah? Are you going to start following Beis Shammai’s opinions?
You ask your Rav. That’s all. In the story you wrote, the Rav told the guy there’s a heter, but it’s not preferable. So, he didn’t follow it. If your Rav says the bourbon is 100% ok, there’s no reason not to listen to his psak. I’ve asked shailos where my Rav differed from some prominent Rabbonim. He said something was 100% ok, while some other Rabbonim hold it’s assur. I listened to my Rav. Had he told me “it’s a machlokes, there is who to rely on for a heter”, I probably would have been machmir. It really depends on how the psak is given over.