I'm not liking this arc very much honestly, mainly because it feels disconnected, out of the blue. While we know that between the 2 nations there is a bit of spite (probably related to this "selling" of land) the fact that this didn't come out in the narration before (unless it did in passing somewhere and I don't remember) seems strange. The arc could have prepared much better by explaining possible policies issues that prevented the assimilation of the former Mulay citizens from the sold zone, explaining how this moved some to banditry, how this group was active (become it doesn't make sense then an active group would not be know, not for people involved in the merchant business) and so on, these bandits clearly have some knowledge on the kingdom considering they did know the emblem.
I'm unsure whatever to consider this a link to the "noble savage" trope. First in the trope the representation is linked to being "untainted by modern society" (modern by that standard obv) that allow them to have an high moral ground, while keeping practices that are considered barbaric. This doesn't seem the case. This seems a group of women, banded togheter to escape society (possibly to escape Mulay rampant misoginy, considering the targetted misandric treatements ) that however had part of society (and so aren't untainted even if by necessity of choice they reverted to a more primitve form of organization and living).
Alas we had multiple represanttion of Malay people, and while I can agree that having a dark skinned ethnicity expressing generally more sexists and misogynisitc views, could be seen as racists, this itself doesn't seems a proper link to the discussed trope. And even if we may be tempted to consider the entire ethnic representation as covertly racist, I'm not sure it would be right.
We aren't on the author mind, so I'm unsure if they decided to have the Mulay people being dark skinned and decided on this arc at the same time. It may even be possible that the arc was decided later, or it was different, for example deciding on having our main couple to being subjected to a bandit attack, and only later linking it to the more general Mulay subplot.
Considering the lack of previous mentions I think it's the last the most probable. Granted is also probable the author is influenced by their own bias.
Also regarding colonialistic mindset... these group is a sort of victim of colonialism. Not the typical one with either military invasions and resettling or spontaneous migrations (for now this idea may change), but one nevertheless. Their territory did change hands (under a bayout formula, like the US did for Alsaka with the Russians, at the detriment of alaskas russian speakers ).
Here this representation seems to be a consequence of colonialism, not a justification for it.
A better presentation could have imho avoided some of this discourse.