Pisteando is a colloquial and somewhat informal term in Mexican Spanish that means "partying" or "drinking alcohol." It's more vivid and specific than just saying "tomando" (drinking).
In the song, the singer uses it to describe his current state: "Y si ando pisteando, traigo la música bien recio" (And if I'm out partying/drinking, I've got the music loud). It captures a specific cultural context of going out and having a good time, often with music and drinks, making it an interesting and engaging word for learners.
This song is about walking away from a relationship that had already fallen apart, and choosing to celebrate instead of mourn it.
The verses describe a woman who is worn out: tired of her partner coming home drunk at dawn, sick of the fighting, and ready to let it all go. The chorus flips the mood. He agrees the flame is out, and instead of chasing her back, he raises a bottle to his chest and toasts to moving on, glad someone new is now in his life.
It plays like a breakup anthem with a party attitude: rather than pleading to get back together, he tells her to go find someone else, because he already has.