Probably you are confused between "drive", "Partition", and "Hard Drive". See, confusion can happen easily!
A "Hard Drive" (this includes hybrid SSHD's, and even SSD's) is a physical device on which you can store stuff. How data is stored there is the next step.
Any empty new Hard Drive must have some basic organization systems prepared on it before you can actually use it. I am not talking about the fabled "Low-Level Format", which actually creates (by recording signals on the blank magnetic disks) the concentric magnetic tracks on each disk surface, and breaks these into Sectors each capable of holding 512 bytes of data, plus some special signals at start and end of each Sector. That most basic work is done in the factory at the time the HDD is made and no user ever re-does that.
The first part of organizing the space on a blank new HDD is to create one or more Partitions. A Partition is simply one contiguous chunk of the HDD's space that will be used and recognized as a "drive" by the Operating System. When the very first Partition is created on a blank HDD, two things are written to particular locations at the very start of the unit. One is a simple bit of code called a "Boot Loader", or maybe a pointer to where that code really is located. If this is the unit that your machine is booting up from, the mobo's OS goes to that special HDD location and loads that code into RAM and executes it. This bit of code actually loads another more capable booting system and that starts the entire process of loading the Operating System. The other special thing is the Partition Table with a very rigidly defined structure and size. It contains space for up to four Partition records (in the older MBR system). Each record has data for exactly where the Partition starts and ends on the HDD, what type it is, whether it contains an Operating System that can boot up, and a few other bits. So the first Partition created causes this Partition Table to be written containing one entry (the first one in the table) for this first Partition.
A Partition can contain as much of the HDD's capacity as you choose, up to its max. Any Unallocated Space can be used to create a subsequent additional Partition. So, you could have ALL of a HDD's space in ONE Partition, or you could split it up.
After any Partition is created comes the last preparation step - installing a File System. This is called "Formatting" which writes to specific locations within that Partition some key files to contain the Directory and all the system files used to track how data files are created and used. In today's Windows System the most common is the NTFS File System.
Once a Partition has been Created and Formatted, Windows recognizes it as a usable chunk of data storage space which it calls a "drive", and gives it a letter name like C:. The names are assigned at boot time, with C: always assigned to whichever Partition was used to boot from.
Many people have developed a habit of deliberately breaking a large Hard Drive into two or more Partitions that Windows will call separate "drives" even though they are all on one HDD physical unit. Why? Well, the biggest reason is preparing for trouble. You create a relatively small first Partition and install your Windows OS on it. Then you create one (or more) much larger Partition(s) to put data and applications on. Much later if Windows gets badly corrupted so that you need to wipe it out and re-Install it, you can do this work on ONLY the C: drive, which happens to be the first Partition on the HDD unit. The other Partition is NOT touched in any way by this action, so all of your applications and data that were on that are still there safely.
In your case, the presence of the SSD portion in your hybrid unit has nothing to do with this overall arrangement. That SSD portion really is used very much like a large fast buffer to speed up disk access. It is managed by the HDD unit itself and Windows does not recognize it as a separate "drive".