I'll come at this from a personal angle. How well do you know this friend, and how close are you two? Depending on the answer I'd *personally* have two different reactions.
If it's a friend that I kind of sort of know, but don't know very well, came up to me and stated "Hey, I heard you're a zoophile. I too like diddling with animals!" I'd likely be freaking the hell out! And more than likely I'd go on the defensive in an attempt to protect me and my girls. As well as ask them where they got that *incorrect* information from for damage control.
If it's someone I'm very close with, like... very close with, and they told me "Hey, I heard you're a zoophile. I too like diddling with animals!" I'd likely ask where they found that information out so that I could try to manage damage control. And if possible, scrub that information from existence. But if I knew them very well, I'd likely come clean about it.