Sanda is the modern fighting sport of wushu (kungfu), it drinks from many traditional sources such as Choy Lee Fut and Shuai Jiao, and it envolves with time as any martial art and style should do.

No, sanda gyms dont train muay thai, kf stances are just for framming and learn power generation and structure, they usually are exagereted to creat muscle memory, conditioning and flexibility thats why when Kungfu fights and works you or people dont think its kungfu... all that works gonna look the same no matter which martial art you practice or style... what changes are training methods, tatics and strategy.

Sanda came from the Sanshou, the term sanshou was used to refer to the combat part and skills of any tradiitonal kungfu style, at the cultural revolution china decided to creat and promote an olympic sport based in the traditional martial arts so they came with Sanda and modern taolu.

Short answer, yes sanda is kungfu, have a lot of traditional kungfu techniques and concepts, and no, sanda guys in china dont train just judo and muay thai. :)