YTA. What did you hope to accomplish by bringing that up? You brought up one niche outlier, and your comment didn't even make sense. I've read this paragraph like three times and I still don't understand your argument:

I then brought up the case of Heidi Falconer, a woman who has a life threatening allergy to the water molecule, to the extent a sip of water sends her into severe anaphylactic shock, and I remarked that if the body really was mostly water that'd be like a person severely allergic to peanuts being mostly peanut butter and it doesn't make logical sense.

Also, you didn't "unintentionally" butt in. You raise your hand and deliberately interrupted him. You have sole control over your actions.