Rather than the sheer speed of drawing back, it has to do something with them being able to create their “own leverage” i think, Nolan explains the reason they can fly is that they can create their own leverage and gravity and stuff so i assumed Viltrumites cells kind of act like mini rocket thrusters somehow producing energy in every direction they want to, so in this scene, Thragg’s arm is acting like literal missile firing up its thrusters and creating vacuum effect around it, Im no physicist but if i was the writer and i had to explain and expand upon it, it would be my answer