Anything in orbit can (and is) actively tracked by amateur and professionnal astronomers around the world. The secret aspect of the X37B plane is it's mission. Nobody knows what it was doing up there. Hypotheses range from carrying weapons, spying, or doing experiments. In any case, it is certainly also used as propaganda, a show of strength.
Agreed with you regarding a show of strength. I can imagine that any release of information is carefully calibrated. After all, the picture in the article with men in spacesuits circling the aircraft is pretty cool. I doubt this is a "leaked" pic...