Carbon is dispersed from the atmosphere wherever it's created. This could be the smokestack of a power plant, a tailpipe of a car, or any other source of emissions. That CO2 floats up into the air and mingles with all the other gases in the atmosphere. Areas that are more highly concentrated with CO2 than others will "push" their CO2 into lesser-concentrated areas, driving up the concentration everywhere over a long-enough period of time.

Drawdown works in the opposite way. By reducing the concentration in a single area, the global concentration would work to equilibrate, so more CO2 would "fill the void", and if more drawdown keeps happening, than more CO2 will keep equilibrating and filling voids, and more capture will happen.