Honguito is the diminutive form of hongo, meaning "mushroom". The use of the diminutive suffix "-ito" makes it a "little mushroom" or "cute mushroom".
In the context of the song, the lyric "Como si un honguito se comió" (As if she ate a little mushroom) is a playful and suggestive way to imply that the person has grown or developed in a noticeable way, similar to how a mushroom might cause a fantastical or exaggerated effect in popular culture (like in video games). It's a unique and memorable image that stands out in the lyrics.
"Honguito" is Dalex and Farruko trading party-anthem lines about a woman who owns the room the second she starts dancing. The verses stack up the compliments the way a reggaeton hook is supposed to: her tan, "Quemadita cuando te da el sol" [Tanned when the sun hits her], her outfit, "En trajecito eso es un 10, eso es un obli" [In a little outfit, that's a 10, that's a must], her dembow. Dalex even admits he can't hold the line here, singing "No soy un santo, tú me vas a hacer caer" [I'm no saint, you're going to make me fall].
The title comes from the hook, "Como si un honguito se comió" [Like she ate a little mushroom], slang for a sudden rush, and the mushroom stands in for whatever she does to a room the moment she walks into it. Pair that with "Si se va conmigo se jodió" [If she leaves with me, that's it for her] and the song stops pretending to be subtle. This is a track built for a party, not for overthinking.