yes, it is. if i send bitcoin and get bitcoin back, it's a mixer.
get your definition of a mixer updated, not all mixers work by blending users funds.
hiding behind buy & sell bitcoin is not gonna change that. the website name is coinmixmarket ffs
The way you use it defines it, you can mix your coins with Binance or any other exchange in the borders of verification, but it doesn't make them mixers. You can sell or buy bitcoin from specific address, so it doesn't mean you making bitcoins clean, it's all depends on your interests.