I was of the belief that Blup refuses to teach it to the chaos knight character every time, so it's nothing new, am i mistaken?
Swimming is of very marginal usefulness anyway so why do you even care?
Blup's quest is overall rather significantly lawful so chaos knights shouldn't bother with it.

Yes, you are mistaken. I care because swimming is of much use. Also I don't want Chaos Knights getting what the Creator did not intentionally want them to get.
Why do you ask? Nevermind, just kidding.

I think it's probably because he changed the dialogue but forgot you can still get taught just by 'g'iving potions to Blup. Blup's a Lawful critter so I highly doubt he'd be interested in teaching a CK any useful skills. Should be changed IMO. (I mean, Blup shouldn't teach it)

Maybe eating a Baby Water Dragon corpse could grant swimming? :)

it grants Water Breathing tho I thought already

If it doesn't it would make sense if it does. Is there a chance for corpse generation?

both water dragons grant water breathing if eaten

Well, there you go then! :) Just eat Blup, then go eat his mum!

If only the corpses were guara- I mean, that's such an evil suggestion.

Might be intentional since this is a rather naive NPC.

Ok, challenge mode: eat Blup's mom in front of him! Or maybe just hand him the corpse and be all "lOoK, I fOuNd YoUr MoMmY! hAhAHaAa!"

If there are special messages for these scenarios, it would greatly reaffirm my faith in humanity. :)

Corpse drop rate for Blup is rather low.

Err... so I hear. <.< >.>

There is room for a small awesome tweak here