"Y'all" didn't originate in Texas. Or, rather, nobody's really sure where it started, but it definitely isn't unique to Texas and more likely came from the Deep South.
Hey, I'm a foreigner, the nuances of American history and regional culture are lost on me. If y'all can call my country "Holland" even though that's like calling the US "Carolina", then I can refer to the entire American South by "Texas".
"Y'all" didn't originate in Texas. Or, rather, nobody's really sure where it started, but it definitely isn't unique to Texas and more likely came from the Deep South.