MCA stands for Malayan Chinese Association. Not Malayan Chinese Party.
This is because when MCA was formed, it was formed as an association.
That is why you have Tan Cheng Lock chairing the inaugural meeting of the Independence of Malaya Party formed by Onn Jaafar. If MCA is a political party, then it would be unthinkable for Cheng Lock to be the chairman of that meeting.
The formation of MCA in Feb 1949 and its conversion to a political party in the second half of 1951 are due to Gurney and Leong Yew Koh, respectively, according to Fernando.
[ p 13, 18 and 19: The Making of the Malayan Constitution, 2002, ed by Joseph M Fernando]
However, a more nuanced explanation is given by HS Lee. [See As Empires Fell: The Life and Times of Lee Hau Shik by Ooi Kee Beng]. Unfortunately, this biography is very short.