Just to illustrate how coincidental it is:
In Akiba there's at least around 10 doujin shops. Each of them has about 2 floors of doujin games. They just happen to be at the same isle, at the same shop, at the same time.
@duylinh well they were in hebinoana(totally not Tora no ana (lol snake hole not tiger hole) ) which is one of the more popular ones so at least its plausable instead of one of the tiny side street shops