XMP typically means running the RAM faster than what the CPU IMC is rated for (e.g. 2666/2400 MHz for latest Intel chips), and motherboard manufacturers will list any compatible memory speeds beyond this speed as "(OC)". ... Yeah technically XMP is an overclock.

Is enabling XMP overclocking?

No matter how harmless it may seem, enabling XMP is still a form of overclocking, just done automatically through enabling the XMP Profile in your motherboard BIOS. Usually, when overclocking, you will be raising the voltage on which your specific piece of hardware runs.

Can enabling XMP damage CPU?

It can't damage your RAM as it is built to sustain that XMP profile. However, in some extreme cases XMP profiles use voltage excessing cpu specifications... and that, in long term, can damage your cpu.