A quick search says cycling lowers the risk by 20% (whatever that means). Gears probably really help here, allowing you to have more resistance with your highest comfortable cadence so you can do cardio.

Either way I don’t think the point is that it is a foolproof prevention (because other factors), but more that the same diet but fully sedentary would likely be worse off. Particularly with the obesity aspect, cycling obviously burns calories and builds muscle (which will raise metabolism) so can help you lose weight in the long run. More is probably better so long as you aren’t really overdoing it or getting injured.