From what I understand of the page that explains this, basically it goes like this:
- They sent the initial 'finished' codex to print.
- Following playtesting, they came up with a new idea for SW Warlord Traits which worked better with their fluff.
- They quickly implemented the changes into every version of the SW codex... apart from the English ones.
So, basically, the PDF page is just correcting a 'misprint' in the English version of the SW codex. Nothing major, as far as I can see.