The "two faced" behavior is condoned by a principle known as
al Taqiyya. The link is written is an Islamic scholar. If you are short of time, the term boils down to bold face lying to cover your real motivation...as long as it furthers the interest of Islam.
Part I
Part II
Part III
The key observation is that you can't trust a damn thing uttered by a Muslim. Lying is ethically proper in their world view.