okay fan theory time
The Ballad of Bilbo Baggins contains the inaccurate statement "he battled a troll!" while leaving out fairly key details of The Hobbit, like the entire Battle of Five Armies or anything around Erebor. Therefore, "in world" the singer is someone theoretically familiar with Bilbo's story but who was too bored to remember less exciting like "teased a dragon alone in the dark," "provided the detail that finally slew the dragon" or "wept for Thorin after a battle which proved friendship means more than greed."
Meriadoc Brandybuck and Peregrine Took. I might have known.