What he probably means is that for a “photo”, an actual act of photography must be performed. While “artwork” can be fully digital. Now, legal definition aside, the two acts are indeed different even if the resulting “image” is a bit-by-bit equivalent. A computer could just output something akin to a photograph but no actual act of photography has taken place. I said the legal definition aside because I know the legal definition only looks at the resulting image. Just trying to convey the commenter words better.
What he probably means is that for a “photo”, an actual act of photography must be performed. While “artwork” can be fully digital. Now, legal definition aside, the two acts are indeed different even if the resulting “image” is a bit-by-bit equivalent. A computer could just output something akin to a photograph but no actual act of photography has taken place. I said the legal definition aside because I know the legal definition only looks at the resulting image. Just trying to convey the commenter words better.
Edit to clarify a few things.