... He thinks individual photons traveling through air should generate sonic booms because speed of light is greater than speed of sound.
I don't think any particle beam would generate a sonic boom traveling through air at supersonic speeds. Seems to me like you need a fairly massive object for that. But I could be off.
In any case, light interacts with air as a wave. Keep in mind that all particles exhibit duality. They have wave-like properties and particle-like properties. Nothing is strictly one or the other. But different interactions can result in one or the other manifesting strongly. Wavelength of visible light being greater than size of molecules in air, and even greater than average distance between molecules, light will interact with air as a wave. Therefore, there are no particle-like collisions between photons and air molecules.
At sufficiently high energies, such as these of gamma radiation, photons will begin interacting with air in a more particle-like manner.