Alejandro O'Reilly, 1st Count of O'Reilly
and his companion Colonel Tomás O'Daly for whom we can thank today for the lovely historical colonial fortresses and architecture of places like Havana, San Juan in Puerto Rico, and New Orleans. They weren't born and reared with those Spanish forenames...they were just nicknames via translating them. Same with William Brown, founder of the Argentinian navy, who went by Guillermo there.
Beto was born and reared in El Paso, TX. El Paso is over 4/5 ethnic Hispanic, and it's also a border town across the Rio Grande from the Mexican city of Ciudad Juárez where people cross the border bridge every day between the two cities and share the news, radio, sports, etc. In fact, it was the site of the Chamizal border dispute between the US and Mexico that was finally settled in the 1970s with territorial adjustments.
In short, he's not Hispanic himself, but he learnt the Spanish language and acquired a Hispanic nickname as a child given where's he from (a Hispanic area bordering Mexico). 'Beto' is just shorthand for anyone with first name ending in 'berto' in Spanish or 'bert' in English, e.g., Alberto/Albert, Roberto/Robert, etc, and since his first name is Robert, he picked up Beto.
There's simply nothing wrong here with him having that nickname given those facts. I've seen people given Spanish nicknames for much less, e.g., an acquaintance from Belfast I once knew who went by the nickname 'Pablo' because his primary school mates stuck it on him because a teacher told him what his name was in Spanish and they liked it.