Yes, I installed clean with a format to Win 7. Since then I have upgraded Win 7 to 8 then 8.1 along with installing Win 10. If it was done as part of an install, as Manny says is possible but not sure, I would think that I would have ended up with something somewhere.
Possibly Manny's other thought about it being something to do with Windows backups. I can't really comment on that I don't schedule any backups. I do them manually doing a fresh image each time.
Ahhh! I bet I know!
A system that comes with a factory OS will be loaded from an image including the OS and added software along with the added partition. If you take a clean drive and partition and format via the Windows installer it is also likely to include a system partition. My case is neither of these.
I initially partitioned for just my install of Win 7, not even partitioning the data drive. I then selected to install on the already existing partition which it did. I then went to drive management and set up my data partition. It dawned on me that I have been using this method since Windows Vista as it was an established way to avoid the added partition.
Oddly, at least in Win 7, the added partition should be only 100MB and listed as a System drive. You DO have such a partition listed as System but it is too large... the size may have changed since Vista and 7. It would be the first, listed and shown as 300MB. As Manny said I would not touch this partition as it includes your boot info. You don't actually need it but better safe than sorry and precautions would need to be taken before removing. To be honest I would not probably bother with anything to the left of the C: unless you just want to simplify and clean up the drive structure. After all what is on the left of the C: is less than 0.003% of the drive if I'm figuring right in my head... 300GB drive, right?