blam,
they also weren't Texans, since there was no Texas!
Texas is a state-of-mind.
Texas was referred to by early Spanish explorers as the "New Philliphines". Nothing against Filipinos but saying that Davey Crockett and the New Filipinos fought to death at the Alamo lacks something.
There's always been a Texas, (well since the end of the long last ice age anyway) it just hadn't been found yet. In fact these folks may have come to North America just as it ended, or even possibly before the last little cold spell really set in (there was a warm spell between the end of the last "long" ice age and the last short ice age known as the Younger Dryas, which only lasted about 1,300 years, and which went from cold to temperate in as little as a few decades.