I asked because cycling outdoors was implied as being a recreation, possibly along quiet roads, for fun. The gym however was the only place where a person could "exercise".
Ah, then there's your answer. The gym person has a misguided impression of road cycling. And of exercise for that matter. Even a recreational, fun, quiet road pootle is exercise.
It's why I couldn't get into spin classes, or gyms generally; I just can't get into that 'work that body', 'no pain, no gain' mindset. I've enjoyed gyms early on quiet Saturdays mornings when I've been able to do things at my own pace, but peak hours or classes where never my thing. Give me miles on roads everytime.