Ultrasound is physical vibration, like waves in water. Radiation is electromagnetic vibration. Similar in concept but different things.
The definition is not limited to electromagnetic radiation.
Once again...
Definition of Radiation
1a : the action or process of radiating
b : the process of emitting radiant energy in the form of waves or particles
c(1) : the combined processes of emission, transmission, and absorption of radiant energy
(2) : the transfer of heat by radiation — compare conduction, convection
2a : something that is radiated
b : energy radiated in the form of waves or particles
Sonic waves are not excluded!