This is a list of astronomical objects with the spectral type Y. They are a mix of brown dwarfs and planetary-mass objects.
Spectral type Y objects are not all brown dwarfs, they just have a similar elemental composition. Jupiter doesn’t have the mass to be considered a brown dwarf, they are 13-80 times the mass of Jupiter by definition.
I guess he’s kind of notorious for saying really obvious things, so it’s a meme to put his face next to super obvious statements or facts.