To be Prime Minister of Malaysia, he has to be a Malay.
So he made himself a Malay by declaring that a Malay is:
Any one who live the Malay lifestyle, speaks Malay, and embrace
Islam as the religion.
So anyone can become a Malay by that defination.
(P.S. Somewhere in this website
is a post that says only Chinese Muslims cannot become Malay. Can't
find it)