certainly the disk drive half. Flash can be sourced from many places. Wasn't aware hybrid drives were still around, I used the early Seagate 2.5" hybrids for several years. Doing a search for hybrid on Western Digital's store indicates they have no hybrid flash/hard disks for sale. Not sure if they ever had one. They do have hybrid storage systems for sale.
Meanwhile(after checking), seems Seagate sells a Firecuda drive that is hybrid, though I don't see mention on the data sheet how much flash the drives have(at least for 2.5", for 3.5" apparently they have 8GB of flash)