Some people wondered about the same question also on Meta Stack Exchange: What's going on with the Announcer badge?, Suddenly getting “Announcer” badges every few minutes?
Recently, some bug was fixed in the procedure that calculated number of visits for purposes of the publicity badges (Announcer, Booster, Publicist). More details are available here: Missing publicist badge? (It seems that problem was with the way links to answers were counted. As the linked post explains, you could now even get several badges for the same question - for example, if you shared both link to the question and also link to an answer. Or links to two different answers.)
This explains why some people received badges now - after the number of visitors from their links has been recalculated. (It seems that Announcer is much more common, but also some Booster and Publicist badges have been awarded recently.)
In some cases, I have got badges for some questions and I do not remember where I shared them. But I'm not really going to lose my sleep over that. (However, if links from chat, meta and the main site do count towards these badges, that would explain some of the cases where I got announcer badge. And it seems that they count at least sometimes, see: I received the Announcer badge for a link to a site-meta shared on a hot network question and Do shared link to ANSWERS also count for Announcer, Booster, Publicist badges? Typically when I post some link inside the Stack Exchange network, I usually post the version of the URL without my user id at the end - but it's quite possible that sometimes I have forgotten to do this.)