Radiology is an imaging technique to diagnose and to treat patients. There are many different imaging techniques that fall in the category of radiology.
One of them is X-ray imaging (X-ray as well as CT), others are MRI, ultrasound and nuclear imaging.
The imaging techniques each have their pros and cons dependent on what is to be imaged.
I.e. bone structures are very well imaged with X-ray, while soft tissue structures are often better imaged with MRI.
I'm not a rocket scientist...pretty confident that an x-ray is a form of radiology.