Seems to be the gist of it. Beckett was waiting on the song, Elizabeth sings it to meet up with the proper people in Singapore, Barbossa mentions the song being sung as an important matter to Sao Feng, so apparently it holds some measure of value to the pirates, and specifically the Pirate Lords. It also seems to be a rallying song, a source of strength to those facing terrible odds, like those about to be hung in the beginning, and the Lords facing down the EITC at the end.

No idea who the kid is, though. Heard a few people say he looks like Young Will Turner at the end, but they looked completely different to me. He did have one of those red herring coins though...so one wonders.