Temperature doesn't exist at the atomic level. It's a measurement of how much movement there is in a set of atoms. At zero Kelvin, there is theoretically no movement whatsoever. In a gas, atoms are moving in all directions and colliding with the container walls all the time (that's pressure), which changes their velocity and direction. They can also collide with one another, but that's much less frequent, comparatively speaking, since gases tend to have very low density.
Now, since the parent was talking about a cloud of "heating gas", it means the gas is being heated in some way. This can happen through a number of different ways, but most of those ways will only act upon a small subset of the full gas being considered. Thus, at any given time, the probably of a random sample of atoms in a heating gas to be of a significantly different speed (that which you call temperature) than the rest of the gas is actually measurably higher than zero, with how high depending on how much heat is being applied and in which manner.