Is that joke that on a cosmic level, it's mostly hydrogen and helium (?) so others get ignored, like how genders other than the usual 2 get ignored? If so, that's so smart and funny, wow.
Yep. Cosmologists work at the largest scale and often simplify regular matter down to hydrogen ("gas") and everything else ("metal").
So if you ever see a reference to the "metallicity" of a star, that can include the presence of carbon, nitrogen, oxygen, etc... which chemists of course would never refer to as metals.
No, there are more elements. But there are only two elements there is an infinite supply of in the universe, Hydrogen and Stupidity, and we're not sure about Hydrogen. /forgot whose joke this was