Do they even pretend to make hard drives? Not in their shop at least: https://eshop.macsales.com/shop/hard-drives/3.5-SerialATA. Perhaps they do produce their own SSD's, as do many companies, since that's trivial in comparison. Definitely not hard drives, though.
SSDs are essentially just some chips (controller, flash memory, and often some DRAM cache) wired together, whereas mechanical drives have many moving parts operating within microscopic tolerances.
For SSDs the hard part is the controller and NAND and there are only a half-dozen companies making those parts. 90% of SSD brands are the same Phison controllers under the hood.