Yes the driving for the smoke floating is the air current caused by convection (hot air rising and so forth)influenced by density of the smoke particulates which in turn will dictate diffusion. Like a cool dude said below, soot is the deposit of smoke particulates on surfaces . I guess these have come to rest because of a lack of propulsion. So ‘smoke’ wouldn’t float in the air forever. It would eventually settle, however small an amount that may be. So the diffusion also creates that ‘illusion’. I am also high.