Non-addressable RGBs, the whole strip/array of RGB LEDs displays one colour at any time. This colour can transition, shift, breath/pulse, etc, across the entire RGB LED colour spectrum - and Mystic light provides a variety of snazzy themes/effects - but every RGB LED is always exactly the same colour as all its neighbours at any given instant, the whole strip is "all or nothing".
Addressable RGBs, each RGB LED (or segment/block of RGB LEDs) can display a different colour and intensity than its neighbours. Some could be lit in one colour or lit in another or more intense or less intense while others are simultaneously displaying something else. Everything that non-addressable RGB does but more fancy animation/striping/chasing effects are possible. Higher cost and complexity.
The MSI X370 Gaming Pro Carbon has 1x 4-pin RGB LED strip connector. That is for Non-addressable RGB lighting. An RGB header is only for lighting, The header has literally nothing to do with fans, and does not have the appropriate pinout to run them. You'd still have to plug the fan part into a fan header.