Boomerang mines user data

I've been interested in using Boomerang, but after seeing this article [1] stating that they "mine user data for information" I'm put off entirely. To what extent do they mine user information? How is this not a direct contradiction of their privacy policy? [2]

[1] https://www.washingtonpost.com/news/the-switch/wp/2016/02/16/want-to-get-more-responses-for-your-emails-write-like-a-third-grader

[2] http://www.boomeranggmail.com/privacy.html