I don't know which topic got deleted and "spam" has a wide definition. I would call it "spam" if the @OP create an ANN thread with referral link, then his next post on ANN thread always mentioning his referral link. Or, the @OP create more than one thread.
But, I'm going to say you're not entirely correct, @OP of the ANN thread are allowed to post their referral link especially gambling ANN where most of them use referral link, try to hover your pointer to their ANN page.
However, if you are using the forum as a publishing platform to host something really substantial and useful, selling ads in that substantial work is allowed. To be eligible for this, your post must be in a topic that you started, and your post must be substantial and long enough to make the ad seem entirely insignificant. If in doubt, ask me.