Beginner Question

White has resigned this game: http://www.littlegolem.net/jsp/game/game.jsp?gid=1558812 but it seems to me that after a sequence like, say, h12n6, m12g12, k8m9 that it's not obvious how Black is going to win. What am I missing?

After h12n6, m12g12, k8m9 (or k8m10), White has no 3-in-a-row, but Black has. So, Black can just place "g10 l7" to create a "4-in-a-row" and 3 "open-ended 2-in-a-row" to win.