Authentic means that it was put on the blockchain by an address owned by the artist. It means that the art could have only come from a specific artist.

As long as it is bit-by-bit identical to the original, authenticity (whatever it means) makes absolutely no difference.

Of course it makes a difference in value. If your neighbor was able to exactly duplicate a Picasso, do you think it would hold the same value as an original Picasso? It wouldn’t. A big part of the value of art is the provenance and the story behind it and the artist.