Less than a minute into last night’s performance, it was obvious the members of the all-instrumental acoustic guitar duo Rodrigo y Gabriela (pictured right), Mexican natives now based in Ireland, care more about Metallica than Manitas de Plata. We can see why listeners mis-label their music as flamenco — it has a rhythmic precision and intensity that are also found in that style. After seeing all the headbanging and devil horns coming from the crowd,…