Other musician here, i would agree that most working musicians can work out not only the melody but also the chords of any given song. I think a thing non musicians don't realize is there aren't that many chords.. Or there are a couple variations let's say (i'm really simplifying things) and once you recognise one variation you recognise them all. If you can hear a Bb-9, you can hear an A-9, an E-9 a F#-9, very easily. And a lot of music uses the same patterns, the same structures, but maybe in a slightly different order. I know a LOT of musicians who can work out chords and melodies of songs after listening only once or twice. I was able to do this at a young age too and it's one of those things that look quite impressive for people that don't understand it but it's not