Hes talking about fair play, not how everyone should change the gameplay due to 1 guy abusing the rules.
Imagine if for just an example, Instead of multiboxing, you could donate money to make your character stronger, lets say give you 200k health and 50k dps.
You need a lot of people to defeat you and its totally unfair, but everyone can do it IF they have money, but it's fine because "blizzard allowed it"
Obviously this dosen't exist because blizzard didn't want people to have such advantage over other player, no matter how much money they throw at the game, it makes for pay to win, and original WOTLK is far from pay to win.
Multiboxing on the other hand back in WOTLK retail was almost never heard of, you could se 5 of them if you were lucky, because people had crappy computers 12-13 years ago, no one could hold up to 40 toons yet alone pay for all those account every month's.
It was absurd and that's why blizzard thought that it's not going to be a problem, we don't have to makes rules against it cause multiboxers are almost never to be seen.
IF wintergrasp battles looked like they do here, on Retail, Multiboxers would have been taken care of long time ago.