I would expect for these numbers to change and reflect the truth with the new Census. Beaumont/Port Arthur are still a mostly First Generation.
First generation what? Hispanic?
In fact, with the slowdown of migration that began with the 2008 recession, more than half the Hispanic population in the metro is US-born or grew up here, so that group is predominately English dominant. The market is estimated in 2020 to be 16.5% Hispanic, and of that about 50% or less are Spanish dominant. That means less than 35,000 Spanish dominants in the market.
Also remember that even in Mexico, not all the listening is to Spanish language music. In Mexico City, music stations that play all or mostly English language music have as many shares as all Spanish ones.
Nielsen does not use the 2010 Census data for ratings in 2020. They use the annual updates to the Census based on a statistical sample done by the Census Bureau and data from Nielsen parent's own Claritas. Those estimates have proven to be almost perfectly accurate, so there should be little change from the 2020 estimates being used now and the results of the 2020 Census, which will be applied to the 2021 ratings.
Nielsen updates all stratification variables every year, including total population, ethnic percentages, age groups, S/E levels, education, etc. They even update annually the percentage of Spanish dominant and English dominant Hispanics.
We have as accurate a population count today as we will when the Census is released. Unfortunately, the Census requires an actual head count even though good statistical sampling, today, is likely more accurate. In other words, I trust the Nielsen estimates more than I trust the Census itself. But the law requires a Census: it is mandated by Article I, Section 2 of the Constitution and must be a full census, not a survey.