must be a residual effect of the upgrade to win 10. i did the same thing and it says win 10 and win 7 for me. but they are both fresh installs. my win 10 was never an upgrade but was a freebie from the insider program.
i'd say it is not a big deal if everything works. but it more than likely will take a fresh install to reset it to say win 10. i have never tried editing this file so i have no idea if you can simply change it to read win 10 in some setting somewhere
edit: i checked 2 other pc's that were win 10 upgrades and they all say win 10 in the bootloader. so not sure what the issue is as it is not really normal apparently. i'd assume if it becomes an issue, a fresh install would be the way to set it right.