Also the whole april fools crowd ignoring that there are a couple different easter egg areas in Reign of Chaos (for the first one anyway, not Frozen Throne, or even the Rexxar campaign that Chen is involved in) for them, one of which shows a picture of an adult male one and a cub.
These are things that would have been in the game for while, not just thrown in as ‘april fools’, just because they make a joke about adding a playable faction of them doesn’t mean what had already been in there was a joke.
Not to mention that vanilla wow has quests that directly say Pandaren exist and are canon, confirming Chen’s existence and help in the WC3 Rexxar campaign: