You may be confusing terms. On ANY storage device there is always one PRIMARY Partition - the first one, usually, in terms of physical location, and the first one listed in the device's Partition Table which contains data on each Partition on the unit. Then there may be other Partitions, all of them called "Secondary". So, the fact that TWO of your storage devices each has a Primary Partition is normal.
Many storage devices also have at least one of their Partitions designated as a BOOTABLE Partition. (Some units used solely for data do not have any Bootable Partition.) Most often this is also the Primary Partition. Whether or not a Partition is BOOTABLE - that is, it contains an OS that can be loaded and run to get the machine going - is one piece of data in the entry for that Partition in the Partition Table of that storage unit. Note that the end of the word is "-ABLE", meaning that the machine CAN boot from this Partition on this storage unit, but it is not necessarily going to do that. Which storage unit and which of its Partitions is actually used to boot your machine is determined by the mobo BIOS at boot time. In its associated CMOS memory chip the BIOS has a default boot drive set, and usually also has provision to allow you to change that choice before the boot process actually proceeds.
You had a system that booted from the HDD which contained an OS in a Bootable Primary Partition. The fact that you have now added an SSD with its own OS in a Bootable Primary Partition did not alter what the old drive contains, so it is still characterized as having a Primary Partition, and probably (unless you destroyed it) containing an OS that is bootable. If you want to confirm WHICH of those two systems actually is being used to boot from, use this test. The "drive" that your machine HAS just booted from is ALWAYS called the "C: " drive by Windows, and other letter names are assigned to other storage units. So, look at the files and folders on your C: and D: etc. drive units. Check also the SIZE of each device. That will tell you what stuff is located on the C: drive, and then you know which unit WAS the boot drive. Boot drive is NOT the same as a Primary Partition.