After a little experimenting I believe that what you're seeing are tracking attempts from websites using the in-app browser.
I didn't see a single tracking attempt when using Boost except when using the in-app browser.
If you click a link to http://amazon.com/ and it loads inside Boost then DuckDuckGo records the trackers that the Web page loads as coming from Boost.
I recommend instead using an external browser:
Settings > General > Default Browser > select "Open Externally"