I don't know if bitcointalk is mentioned on some SEO/SEM forum/community but some time ago these sort of spammers started popping out seemingly out of nowhere.
Bitcointalk has a lot of visitors, good rank and is an authentic site. A lot of people looks for such forum which is active and post links to get visitors and/or to get back links. Most of the times, such spammers only follow the instructions given by their employee from different marketplace. They are given some forum names and what to post in brief.