It's possible that when Baudhāyana Dharma Sūtras were being written, the Kaliṅga region was not ruled or conquered by a Kṣatriya king and cāturvarṇya (system of four castes) was not established there.
Commenting on Manu 2.23 this is what Medhātithi says:
Similarly, if a certain well-behaved king of the Kṣatriya-caste should happen to defeat the mlecchas ...
The same page gives a justification from the Apastamba Dharma Sutram
Let him not visit inferior men (such as Niṣādas), nor countries which are inhabited by them.
Also, Manu Smriti parvam 4:
Let him not dwell in a village where the sacred law is not obeyed, nor (stay) long where diseases are endemic; let him not go alone on a journey, nor reside long on a ...
Mt. Semeru is located in Indonesia.(https://en.wikipedia.org/wiki/Semeru) India and Indonesia have a lot of common culture. And Indonesia was like an extension of Indian kingdoms before the Dutch colonized Indonesia and British colonized India. Hinduism was the primary religion in Indonesia before Islam became dominant.