Hynix (and Samsung, and Elpida and Qimonda and Micron) do not sell to the public. They make modules and chipsets that they sell in bulk to manufacturers and to RAM assemblers and rebranders.
So when you buy an Apple machine, it may have Hynix or Samsung or Micron modules in it, Apple uses their suppliers interchangeably.
When you buy a name brand memory module from Crucial or OWC or DMS or whomever, it could be made with Hynix or Samsung or Micron chips. Buffalo manufactures their own modules, but not the chips --they buy the chips from one of the major foundries (the chips are private-labelled for them). If the foundry makes both the circuit board and the chips and assembles them, it's called for example a "Samsung Genuine" or "Samsung Original" module. If the module uses a third party circuit board with a major brand chipset, then it is called "Samsung-on-third" memory.
(Crucial is owned by Micron but they do not use exclusively Micron modules, although Micron makes the majority of their modules they also rebrand Samsung and Elpida and others)