People often pay a premium for something that is not worth the extra money...that is the definition of Beats headphones.
The other definition of premium is analogous to high end. That is the opposite of Beats headphones.
I'm not mixing them up -- they are all valid dictionary definitions of the word.
When people say "premium" in reviews they usually mean "on the expensive side", and regarded as more exclusive with regards to brand, constuction etc.
The same way clothes are called "premium", because they belong to some well known expensive brands, despite being made in China and being totally crude and workman-like compared to fine clothing from a tailor etc.