The fact that they can detect that you're using the TOR browser configuration isn't that shocking when they also see that you are coming out of a TOR exit node,

The fact that they can detect that you're using the TOR browser configuration isn't that shocking when they also see that you are coming out of a TOR exit node, or the site you are loading is an Onion site. The anonymity comes from looking like every other person who downloaded Tails.