Kung Fu is known to many as martial art. Kung Fu tea therefore is related to martial art by default. Perhaps tea drank by martial art practitioners is called Kung Fu tea?! Perhaps tea must be drunk while making Kung Fu moves?!
Kung in Kung Fu tea is different from Kung in Kung Fu in Chinese writing and meaning. Although both pronounce the same, they actually take on different meanings.
Kung Fu Tea : 工 /work/worker/skill/profession/trade/craft/labor
Kung Fu: 功 /merit/achievement/result/service/accomplishment