What you experienced is not uncommon. There are a lot of people who like to think they're "in the know" about things they know little or nothing about.
Years ago, I had a co-worker whose brother was a JW. Our co-worker invited our boss to a social event where her JW brother was present. There was drinking. My boss came to work and said to us something like, "and her brother was drinking with us. I didn't think JW's were allowed to drink." Another co-worker, a know-it-all type, responded, "You're right. There are two things Jehovahs Witnesses do not do, drinking and card playing." Again, she was thinking about Mormons.
In their minds, the cults run together. It's like I hear people getting French words and Spanish words mixed up because they've never formally studied either language, and they're repeating wrong information given to them by someone else. Instead of correcting them, I say, "That doesn't sound right. Let's look it up."
When I was "studying" with the dubs, the people who "studied" with me lived two doors away from the Kingdom Hall. Once their house was up for sale, and a prospective buyer asked them if they were bothered much by those "old" Jehovah's witnesses. LOL