I'd write them a brief, but not unkind note, introducing yourself, and saying

"No, I don't have 11 million cats, I don't even have 11! But the other coment I overheard was right. Besides my full-time job as a school teacher, I do volunteer work witha cat rescue organization. As a matter of fact, I even have one cat I am fostering who was flown here from Bahrain. I know you're new to the neighborhood, if you are away from home and cats that you miss, you are welcome to visit with mine some time. But don't ask to pat the Bahrainian foster - she has teeth and knows how to use them. However, if you need a ferocious beastie for one of your theatre productions, Ally'd fit the bill!"

That way, they both know the truth, and know that they were overheard, and can choose to either be friendly, or at least keep their mouths shut next time.