'-Coded' is a suffix that means 'giving the vibes of' or 'reading as'. 'Cottagecore-coded' means something has the vibes of cottagecore aesthetic; 'gay-coded' means a character or person reads as queer without explicitly being so. If your teen calls something 'X-coded', they are making an observation about aesthetic or identity signalling. Harmless cultural-criticism vocabulary; useful for thinking about how things signal meaning.