yes it is 100% true. kela comes from Ahom word kla which inturn comes from Burmese word Kalar (meaning Indian) which inturn comes from the Pali word Kala meaning dark or black. the ancient name of India in Tai was merng kla or the country of kelas... originally the ahoms used to use this word as abuse and soon common people started using it too without knowing that it was a slur for them only... you can read the article on kela for more information