Se prendió el cerro literally translates to "the hill caught on fire". It's a popular Mexican idiom used to say that a situation suddenly became chaotic, intense, or out of control, similar to the English phrase "all hell broke loose".
In the song, the artist uses this fiery expression to describe the exact moment his girlfriend checks his phone and a massive argument erupts. It’s a vivid and dramatic way to paint a picture of sudden trouble.
This song is a wild ride through a very messy love triangle! Neton Vega kicks things off by repeating, "Son mi suerte y también son mi muerte" [They are my luck and also my death], which perfectly sets up the drama. He's talking about two women he's involved with at the same time, admitting, "Sé que no debo, pero a las dos las quiero" [I know I shouldn't, but I love them both]. Of course, this doesn't stay secret for long.
He describes the moment one of them finds out by looking at his phone: "Me checó el cel, se prendió el cerro" [She checked my phone, all hell broke loose]. He calls her a "pinche vieja loca" [fucking crazy old lady] for getting angry. It seems she's accused him of being a "perro" [dog] and letting money change him, and is now trying to make him jealous with someone new. But he plays it cool, talking about his expensive clothes, waiting for his birthday, and planning to celebrate with whiskey and tequila. Throughout it all, he keeps coming back to his physical attraction, wondering, "¿qué tienen esas nalgas, esas tetas?" [what do those butts, those boobs have?]. It's a blunt and chaotic story about desire, getting caught, and trying to maintain a cool, rich-guy image through it all.