Nope: doujin means something along the line of "homebrew" in Japan: doujin manga is HUGE and there's a pretty big scene for doujin games as well. Any game labeled "doujin soft" essentially means PC homebrew from Japan, usually coded as hobby projects in bedrooms by a few guys. Most of the weird eroge stuff qualifies, even if it's on sale in stores.
It should be noted that a disturbing amount of doujin content, games, manga, animation, whatever, involves humping, often with tentacles or the cast of Gundam or Evangelion. This can be explained as "Japanese Otaku Culture".
Sometimes a doujin game or franchise can end up becoming something more: Melty Blood (actually, most if not all the Fate/Night stuff) and the Touhou games are examples of this.