The asset is more akin to a deed or a claim. Most NFTs are images hosted on S3 or IPFS. The blockchain entry is metadata with a pointer to the hosted asset.

The NFT is the metadata. The metadata is the token that cannot be funged.

The image is a wholly separate thing that a token points at, and multiple tokens can point at the same thing just fine. NFTs be be funge-free but images are fully fungible.