This image is racist because Tom has east Asian caricature features of the buck teeth and closed eyes, and is in a cartoonishly small bed as east Asian people are often shorter compared to the western average height. My first thought was the the joke was that Tom has to squint, another racist trope, because the poor video card can't handle the high resolution.
My second thought was that he was too big for the bed, which appears to be the actual joke. Sadly it was spoiled because of the overt racism in the chosen image so it just got a chuckle for the real punchline.
That person is wrong here, but I think they were thinking about other scenes. There's a few of them on youtube if you search Tom and Jerry stereotypes.
For those who don’t want to click through, Tom is hit on the head by a woman (an actual racist caricature named Mammy Two Shoes) and starts to think he’s a mouse. He grows buck teeth (like a mouse or rat), starts eating cheese, and attempts to sleep on Jerry’s bed (as seen in the meme).
It’s important to recognize racist stereotypes, especially with how prevalent they were in old cartoons, but it’s also important to avoid jumping to conclusions and calling out problems that aren’t there.