Board Thread:False Info and Speculative Discussion/@comment-5237598-20160303134759/@comment-26879545-20160303143837

The Beast was learning while it was trying to remember its true identity. Maybe the DD's mentioned the Argents in passing and the Beast took it in because it sounded familiar.

Maybe he assumed they were Argents because Marie-Jeanne said that history would know him as "The Beast;" so for someone to say they know his name, it would be a logical conclusion to reach. The only people that would really remember (or hear about him) would be descendants from his sister.