Noted in the
OA thread too. I mean, it's a little different from WB's:
The cartoons you are about to see are products of their time. They may depict some of the ethnic and racial prejudices that were commonplace in American society. These depictions were wrong then and are wrong today. While the following does not represent the Warner Bros. view of today's society, these cartoons are being presented as they were originally created, because to do otherwise is the same as claiming these prejudices never existed.
But yes, very strange. I'm hoping this is a placeholder for a more thoughtful response, but I wouldn't place bets on that. (Particularly since they also put the disclaimer on every single pre-5E product, which feels like future-proofing more than anything else.)