Dreaming of better days
Oh, they make note of that plenty of times in the source. And his mother, whom he inherited it from, actually did play it like a cello. Him swinging it onto his shoulder and playing it as a violin is part of his signature gag.
Yeah, like Zef says, it's kind of a running joke in the original story...also, there are other characters with totally absurd musical instruments. Toward the end of the game, you meet Raiel, a childhood friend of Hamel. He carries around a solid gold piano on his back.
Turns out I was in fact missing a joke. Fair enough!