Malabar is the name given to the south west coast of Indian Peninsular. Initially used Arabs as regions of Gujerat, malabar and maabar to denote the coastal stretch of India form the northwest to South East are south of Kollam was the transition between malabar and maabar.
the British later upon the their conquest and direct rule over the northern part of current Kerala and the indirect rule over the princely states of Kochi and Travancore decided to name above mentioned northern kerala as Malabar District and put it under the Madras residency, only to merge with teh southern princely states under the name Kerala in 1956.
the term malabari to name a race /people is mostly used outside India, by the people who knew the regions earlier. the Arabs refer to all malayalis as Malabaris.
In Malaysia where most Malayalees setteled bfoer 1856 , teh termis still being used but in a different context.
The earlier generations used in to differentiate the Malabaris from the Southern Keralites. the current usage however refers to the Muslims from Kerala, probably because the earlier migration to Malaya were mostly Muslims from the Malabar District.
So though its a misnomer, the term Malabari is used as a race as well.
Knowing history helps to see how and why it happened.