This is a breakup song with a smug little grin. The singer's ex has moved on, or at least wants everyone to think so: she dyed her hair and started wearing miniskirts, and he reads it straight away. "Te tintaste el pelo y conozco la intención" (You dyed your hair and I know what you're after).
Then comes the hook. "Me dijo un pajarito" (A little bird told me) works just like the English saying: someone passed him the gossip that she still checks up on him and misses him, even while she "se hace la fuerte" (acts tough). He's sure all the fun photos she posts on Facebook are a show, because "sin mí tu vida es aburrida" (without me your life is boring). It's cocky, a bit much, and that's exactly the charm. He even jokes that she can have family, friends, suitors and "un perrito que te ladre" (a little dog to bark at you), but she still needs him "para portarte mal" (to misbehave).