RHEL kernels are like that. They backport a ton of stuff and the major version number is of little relevance, but it doesn't change because they maintain a stable kABI.
By now the CentOS 7 kernel is probably closer to mainline 4.x and 5.x than the original 3.10
Wait until you find 2.6 (not many changes before 3.2 allegedly) and 2.4 kernels in embedded systems.
what the actual f*?
Even with stable fixes and CentOS distro sugar on top, running 3.10.x in 2020 feels batshit crazy. I always thought such reptilian kernels are only found on shitty embedded devices...