I’m not sure they are talking about ACTUAL towers - just what is perceived by your phone to be a tower. Could be some transmitter in the black van parked across the street from the local KKK or Islamic prayer meeting. Or perhaps a transmitter hidden amongst all the other antenna on an actual tower. I’m just guessing though.
You are correct, it’s called “Stingray” and could be mounted to a existing cell tower, but more likely used in an undercover van or other vehicle. See:
http://www.freerepublic.com/focus/f-chat/3197737/posts
and
http://www.usatoday.com/story/news/nation/2013/12/08/cellphone-data-spying-nsa-police/3902809/