Billionaire Elon Musk and his 2-year-old son X Æ A-12 were seen roaming the grounds of the Sombrero Festival in the South Texas town of Brownsville on Saturday and mingling with common folk. The recent-ish Texas resident was caught scarfing down a spiropapa — a fried, spiral-sliced potato on a stick — at the annual festival celebrating Texan and Mexican culture, according to multiple social media images.…