Marcus, I’ve noticed sometimes people will let their blogs lapse, then let their domain names expire. Sometimes it ends up at a parking page, and sometimes a spammer snaps it up because it already has incoming links. That could be what you ran into. Or it could have just been really sneaky spammers.
I saw one a few weeks ago that led me to coin the term, link laundering (like money laundering). The commenter’s blog looked perfectly normal, except every single link in it was to the same spam site.