"Wushu" in literally means 'martial arts' in Chinese. I don't know if that has a contemporary, narrowed meaning now. I'm guessing it's just the general term used to mean Chinese Martial Arts, and the instructors just teach you whatever sub-category they are willing or capable of teaching.
For all intents and purposes, 'Kung Fu' and 'Wushu' might as well be synonymous. The former's simply a Cantonese phrase.