So a painting, music, video game NFTs are all uploaded to the server but the blockchain is only there to confirm authenticity of product via digital signature?
Pretty much; and pretty much just a proof of ownership to the "original" one. Sounds really stupid at the surface level but I don't know, maybe some smart dude can make something great out of the concept. Some people are calling for digital tickets(like how you can collect old vintage concert tickets) or something.