Callo literally means "callus," like the hardened skin on your hands or feet. It's an unexpected word to find in a song, making it quite memorable.
In the context of this song, it's used in the phrase "Es un callo de verde," which is a slang term. Here, "callo de verde" refers to a large wad or stack of money, specifically US dollars (greenbacks). It's a clever and unique way to talk about wealth, hinting at the hard work and perhaps even the rough nature of acquiring it, much like a callus forms from repeated friction.
Aldo Trujillo's "Cuento Quemado" is a blunt and confident declaration of success and independence. He starts by saying he's not just some nobody, but someone who's made it big, even if his past is "cuento quemado" [a burned story] or old news. What matters is now, and he's grown up negotiating.
He makes it clear that he's a force to be reckoned with, known in places like New York and Las Vegas. Aldo laughs at those who doubted him, remembering "todos aquellos que se pasaban de lanza y ya vieron quién es su patrón" [all those who crossed the line and now see who their boss is]. He's not flashy with clothes, but he's well-received, and he's got "varios millones" [several millions] to his name, seeing his success as blessings from God, not pacts. He warns people to watch their tongues because "muchos rumores se escuchan y acechan" [many rumors are heard and lurk].