Good!
This is what he got for wearing offensive words in public.
I bet they would have banned him if he had said that about anyone. The 4-letter word was what was offensive.
I think you're exactly right. Southwest Airlines is also one of the more family friendly airlines, meaning lots of families with children fly with them. If I were a parent of a younger child sitting on that plane and this bozo got on I'd have gotten up and asked him to use the lavatory and change his shirt first.
Barring that, it is well known that the Captain of every plan has the authority to remove passengers from the flight if he deems them to be a danger, or disruptive to flight operations either before or during the flight. (Would've been nice to chuck this loser from the plane in flight, btw.)