The meme is a picture of him with the cigar in his mouth as he says it the line, so it makes sense to change it to "earf". It would make exactly the same amount of sense if the character was white. Maybe there's some accidental racial connotations that non-American audiences might not understand, but all the people saying "he doesn't actually say it like that in the movie", as though that matters, are missing the point as well.
The meme wasn't created with the intention of changing the context of the quote, it was created from a false memory of the quote, a false memory instanced in part from the racist idea that a black person would say "earf" instead of "earth" because of AAVE. If that was a white character who had said the line, I guarantee that the text would have read "welcome to earth" because there would be no reason to imply a mispronunciation.
All of that said, on a scale of 1-100, this is like a... 5 racism. It shows a likely unintentional bias but the person who created the meme probably hasn't read the Turner Diaries if you know what I mean.
WE'RE GETTING OFF TRACK THO:
Slavern please consume anything other than contemporary popular nerd media.