I am newbie in Linux and I am trying to understand the basics of the Linux OS structure.
So: Are the 'linux-kernel-modules' listed in the output from 'lsmod' and 'GNU C Library' (about 2000 subroutines) one and the same thing/s?
No, Linux kernel modules and the GNU C Library are not the same, and I don't know where you got that idea.
The kernel modules are parts of the Linux kernel that can be loaded on demand. Depending on the configuration there can be thousands of modules, and a typical installation will only use a few hundred, but it depends on the hardware and other things which of those modules are used.
The GNU C Library on the other hand is a collection of C function for user programs and is not used in the kernel.