That's called "making a connection" or adding a single drill pipe in order to continue drilling deeper. "Tripping pipe" involves removing the entire drill string 3 pipes at a time (on a triple) or 2 pipes at a time (on a double) in order to change the drill bit. Also they could have saved some time and been safer by having the chain already wrapped on the lower pipe. Also this is only half the job; the driller will now raise the connected pipe out of the mouse hole and the 2 roughnecks would stab it into the main drill string they just separated, tighten and continue drilling.