Research has already proven that it's genetic so they have to invesigate further in order to find missing pieces of IBD so they can cure it someday.
Smoking can aid with keeping UC at bay due to the fact that carbon monoxide via smoking has an anti-inflammatory affect on the colon...hence it can trigger UC in a person if they quit smoking...therefore it is considered that quitting smoking leads to being a trigger for the development of UC...not necessarily for everyone that quits and is predisposed to gettin it, because everyone's trigger(s) varies from one another...that is why I think researchers are having a tough time figuring this disease (IBD in general) out.
And it's true, there's no way anyone here can rule out genetics because you simply will never know all your ancestors health history, let alone their bowel habits....it can be passed down from great, great aunts, uncles, grandparents, cousins, etc...it's not necessarily passed down from close generations...it can skip generations as well.