I would tell them "you can't control IBD anymore then you can control getting a sinus infection, headache, etc... It's an internal disease not caused by me. If you're more interested about my condition, there is a ton of info online, look it up". and I would leave it as that.
What I have learned is that there are SO MANY people who lack common sense and say things that just don't make sense. You just have to realize this and not be sensitive to others ignorance.
Glad you are feeling better!