The rule you are referring to isn't about airdrops, please read what theymos has written about it:
Most giveaway threads are no longer allowed in the Alternate cryptocurrencies sections. From now on, posting or replying to such threads could result in being banned. Existing threads will be locked.
Specifically, you are not allowed to give people any incentive to post insubstantial posts in your threads. You can't offer to pay people who post their addresses, usernames, etc. You can do giveaways off-site and link to the giveaway page in a thread, but you can't give people any bonus for replying to your thread.
The rule is about on-forum giveaways or providing incentives to users making posts in your threads or asking them to post certain stuff to get a reward from you, and it specifically says that you can do giveaways off-site and provide a link to the giveaway page in your thread.
So, since airdrops are almost always off-site and no one is paid to do tasks within the forum, I don't think the forum is against them. However, I still don't find any reason for theymos to create a separate sub-board for such things.