 I don't think the third sentence is intended to explain the second one.   The article is correct in saying that use of UKP is incorrect because it's not the ISO symbol for the currently.  However, you are correct in that the ISO code is a bad code - UKP would be a far better ISO code because of Northern Ireland.  When I quote a code for a currency, I use UKP for this reason.  However if you are looking for the code in xe.com or other places that use the ISO codes, you'll need to look for GBP.   