If a blog post features a twitter post, as recently that post from the @Minecraft account:
https://twitter.com/Minecraft/status/854590419375595520
...then the title of that blog post (as it appears in RSS readers) contains two @'s before the user name: "Featured tweet by @@Minecraft". This is either a one-time error or it happens every time a twitter post is linked.

This can be seen in both the RSS feed and the Atom feed, even in the raw content of the feed.