Moody/BCJ doesn't actually say that they are both Death Eaters he just says Snape need to be careful and since Moody knows that Snape was a death eater that makes sense So he doesn't give away that he is actually BCJ. As for your 2nd point It is a spoiler. Have u read all the books yet?

^this

Hah thx

Thanks.

I have read all the books. Finished the last one about a year ago. My mum is reading GoF right now and asked this question. So, cheers!