Fast wave propagation does not require fast motion of the medium itself.

Evidence

Fast wave speed does not imply fast motion of the medium carrying the wave. Legions of adjacent small pistons can play the role of the arms of football fans and create potentially fast-moving collective waves while never moving very fast themselves. The speeds attained by vibrating surfaces are normally not very high, even if the waves moving along them are fast: If a section of wall is vibrating in and out as a whole so as to create a very loud, 94 dB, 1000 Hz tone, it has to move at a maximum speed of only about 2 millimeters per second! — Eric J. Heller, Why You Hear What You Hear- An…, 697

Categorization

• XREF: Connects to the classic ‘wave on a rope / stadium wave’ distinction between wave speed and particle speed, also central to water-wave and string-vibration pedagogy.
• CANDY: The stadium-wave analogy plus the vivid ‘2 mm per second’ figure makes a great dinner-table fact about how sound really works.