FYI, the clouds aren't pushed away, they are created by the difference in pressure the shockwave (temporarily) creates.
Waves in general do not move matter (except for the temporary oscillation).
Just to expand on this (pun intended), a sound wave is just a change in the local pressure of the fluid it's going through. The rapid and sudden pressure drop across the leading edge of the shock wave causes vapour in the air to condense and form clouds. This happens because lower pressure air has a lower temperature (in this case, because it cannot reach equilibrium fast enough) and lower temperature air holds less humidity. That humidity is the vapour that condenses.
You'll see this same effect on some jet fighters going transonic, contrails from wingtip vorticies on aircraft and other various natural phenomina.
I am sure you are right about the apparent cloud movement in this case, but shockwaves can result from sudden displacement. I read somewhere that Fermi made a good estimate of the Trinity bomb yield by dribbling a stream of shredded paper from his hand. After the shockwave passed him, he paced out the displacement of those that were in the air at the time.