The GF cloud computer is sending data, not control signals. This data could take several forms. Sending a block for each motion of each stepper would be incredibly inefficient but GF may be doing it that way. What I take issue with is the claim that there is no control board. That statement is absurd. There must be some electronics to turn a raw digital data stream into stepper motor pulses and that electronics must be local to the machine. In fact, I saw a tear down of a Glowforge machine on the internet the other day and the control board was clearly visible.
It is unfortunate that Glowforge designed a machine with so little intelligence that it is worth nothing without a reliable and high speed internet connection and the existence and support of a small shaky company. The company advertises this gross deficiency as if it were an advantage.