Because the air inside of compressed air tanks can have moisture in it, I would also swab with alcohol and dry patch after the air is forced through the bore.
The moisture is the reason that the compressor maker's recommend that the air be released from the tank after each use, so that the interior of the tank doesn't rust. Whenever I open up the air valve located at the bottom of the tank after use, some water comes out at the very end. Perhaps the high air pressure causes condensation inside of the tank that can also find it's way up through the hose. It's probably not a big deal since it's such a small amount of moisture. But if you're going to swab with alcohol anyway, might as well swab with it after the moist air is used.