For Muslims Mushriks are those who are making shirk with Allah. But for shias?

Imam of shias in ahadeth, Muhammad al-Kulayni narrated in “Usool al-Kafi” (p 279):

من أشرك مع إمام إمامته من عند من الله من ليست إمامته من الله كان مشركا بالله

Translation:

From Imam Abu Abdullah: Who would makes shirk with Imam which Imamah is from Allah by the one whose Imamah isn’t from Allah is MUSHRIK IN REGARDING  ALLAH