I can easily imagine Facebook's machine learning algorithms picking a signal out of this data and using it to target ads. They may not have had to tailor a query to search for "size of tax deduction". The machine learning algorithms did that on their own. In a completely opaque manner.
I doubt it is anything anywhere near that fancy. Look at the primary source of this complaint, which is available in GitHub. One of the sites was putting sensitive data, such as income amounts, in the page title. The Facebook analytics thing sends the page title to Facebook. Google Analytics also takes the page title. You can easily see how any old targeting engine, machine inference or otherwise, would take the titles of visited pages as a signal.
