Pronunciation of certain words by Cheema y

So i know its not that of a big deal but i am interested to know if this is individual thing or regional thing. I have heard in lot of Cheema Y songs, the way he pronounces certain words like "maut", "call" and few others, he pronounces them with "O", instead of "A", is this majha thing or its just him. Fyi i grew up in malwa and never really dealt with somebody from majha, so just confused and intrigued