The comparison was to say that it is a rash judgement/overgeneralisation about people one has never met, based on hearsay. The implication was that Comorians were the most likely source of crime when there is no proof. Any question about demographics and who is immigrant who is not ws largely irrelevant to my question. After all, negative judgements about creoles by immigrants from Metropolitan France are no better. The same would also for two communities that have lived alongside one another for centuries e.g. Christians and Jews in Europe.
Of course, people could say 'they probably had spiky hair' or some other stereotype or overgeneralisation. Or people could say 'they were likely low-status young men with self-control and anger problems and exposed to violence at a young age' which would probably be correct across social/ethnic situations, across humanity basically.
One similarity is that there were more Mexicans in the US beforehand, particularly in the South, as they were previously Mexican territories and more Comorians a century ago in Réunion
There are differences between the two scenarios though, most notably that the population of Comorians is a lot lower (0.3% of the population) and that Comorian culture is close that of the ancestors of Réunionese people. So basically it's like 'you're too much like my grandfather'.
As for demographic shift, we can distinguish between shift in racial origin, identity and culture. These shift at different rates from each other, depending on the status of the immigrants involved. High status/powerful immigrants will make a much more rapid change in culture, and belligerent immigrants i.e. invaders will make more pajor structural changes.
If we look at a case like Mauritius, the population was long majority Afro-descendant, and is since the late nineteenth century majority majority Indian descendant. But the main language stays Mauritian Creole, and the main music genre stays sega, even if the majority religion has changed. Similarly, in the US, Latinos are generally more and more anglophone unfortunately.
So that brings us to a second difference: Mexicans influence the general culture in America to a greater extent than Comorian lunfence on Réunionese culture at the moment.
Of course I can understand it can be annoying for foreigners to have more chance at getting a job than you in your own country, but Comorians are not in the least bit priority for school or house places, let alone jobs. If people are looking for where do all the jobs go to, the obvious target would be people from Metropolitan France, who are demographically more numerous and more often employed, more highly placed when employed.
I'm not saying mass immigration is necessarily a good thing (it would generally be better to resolve the problems of inequality and negative self-image in the home country),
And its important to keep one's culture, but I'm not sure to which extent the culture of Langley Park differs from that of other Anglo-American neighbourhoods.
So basically my comparison was intended to be about not being a dick to people who've never met based upon stereotypes of their origins, whatever the demographic or immigration situation.