Had to look this up, because I’d seen it before but didn’t want to accuse Americans of being crazy without proof:

https://www.merriam-webster.com/dictionary/hamburger

1 a: ground beef
1 b: a patty of ground beef

The meme says singular “hamburger”, so it makes sense that they meant it in the ground beef sense. Every other dictionary starts with “a patty of ground beef” by the way, so it seems to be an American peculiarity.