[Anechoic]

It's all waves.

EM waves vs pressure waves, they're not the same thing (although the math is basically the same, just with different constants). Something that affects an EM wave won't necessarily affect a pressure wave - a Faraday cage for example will block EM waves but won't do anything to block sound waves.

[sirclueless]

EM waves are transverse (they oscillate perpendicular to their direction of motion) and sound waves are longitudinal (they oscillate in the same direction as they move).

There are some mathematical differences between transverse and longitudinal waves, so it's not just the same math with a different medium.