I would think that they're lying, too, except that they told at least two seperate members here that it's not their ad. It could be because they knew they were going to get into trouble and wanted to deny everything. It's hard to say. Perhaps someone wants to get back at you and them, too.
But, this isn't the first time that someone's photo from BYC has been stolen to use in a Craigslist ad, but it does seem strange that they've stolen so many of yours.
If they try to use one of my photos here, they would definitely be in trouble. All my photos are of feral waterfowl, lol.