It’s only one sock?
In the Box:
** (1) Cotton Compresion Cushion Sock, Black, Medium*
The package also spells “compression” correctly.
TBH, you will often find them sold that way at the pharmacy. There are indeed many reasons to purchase/wear only one.
Occasionally I’ll grab a pair when they are on sale (well, used to, I now have nearly 3 dozen pairs from woot 
) and to this day I have a brand new “single” odd one. Picked it up years ago thinking what a great price for a pair but it was not a pair 
.