If the argument is about dutch, then have an opinion from a dutch person: It's not racist, it's funny.

They are probably presuming it's intended to be AAVE or similar.

I didn't know what AAVE meant, so I asked Wat dat: https://drive.google.com/file/d/11-S_eJt42MJwvMsnnPP43I6DfAW...

Anyway, I want to be clear that I didn't mean to offend anyone. It was just a coincidence.

Of course, you are totally fine. Even with that interpretation, shorthand slang pronunciations have definitely become enough of a part of common parlance especially on the internet that it is quite a stretch to invoke potential racism.

Hell, 'Wat' has its own Know Your Meme page, as do several phrases including 'Dat' https://knowyourmeme.com/memes/wat