The snap you posted have no relation with Asynchronous Circuit .
"Most digital devices today use synchronous circuits. However asynchronous circuits have the potential to be faster, and may also have advantages in lower power consumption, lower electromagnetic interference, and better modularity in large systems."
Read the first paragraph here -> https://en.wikipedia.org/wiki/Asynchronous_circuit
Also search for this line too " Since asynchronous circuits don't have to wait for a clock pulse to begin processing inputs, they can be faster than synchronous circuits, and their speed is theoretically limited only by the propagation delays of the logic gates. "
So combining all these is it not clear that Asynchronous circuit is faster than synchronous circuit ?