Gostoso literally means "tasty" or "delicious" when referring to food. However, in Brazilian Portuguese, it's very commonly used to describe something or someone as pleasurable, enjoyable, or even sexually attractive.
In this song, the opening line "Quem é que faz gostoso" uses gostoso in a suggestive way, implying someone who is good at lovemaking or provides intense pleasure. It's a word with a dual meaning that makes it intriguing and culturally specific to learn.
"Sou Eu" is a playful, flirty forró hit by Wesley Safadão. The singer is teasing an ex who still can't quite get over him: he's the one who "makes it feel good" and lights her fire, and no matter how she plays it cool, she still remembers exactly who he is.
In the second half, he spots her on social media with someone new, posting cute couple photos and captions. He isn't buying it, though. He teases that her new partner can't possibly measure up in bed the way he did.
It's a confident, cheeky song about an ex who is sure he left a lasting impression, sung over a driving forró rhythm made for dancing.