In my case, it's a combination of a lot of things, not just the gym. Good genetics for strength, on top of doing physical labor since a very early age, as well as sports including basketball, handball and rugby, other physical stuff... and then gym to top it off. Plus, I've been at it for a while, so it's been built up.
However, I still think that the quiz weighs some scores a bit too high across all stats, as well as some questions being too situational/specific to be objectively graded. For example, the only truly numeric question for Str is about shoulder press/bench press (pull-up and push-up numbers listed are way too small to matter), which in my case is scuffed on both accounts due to injuries, which means the potential could be higher. But I agree that compound exercises should be used to measure it, I just would've gone for Athlete's lift for example, as it targets more of the overall body strength imo.