Not defending the guy because they obviously stole the assets (the file names are the final nail in the coffin) but that's not his argument.
He's claiming that they didn't copy the assets but inspired themselves from them. He's claiming that they (just like everyone else) are building upon the shoulders of giants.
That argument is perfectly valid, until the accusing party pulls your files named after their own bosses (carrying the typos along too). At that point, you've pretty much been proven wrong.
It's a perfectly valid argument if it's over game mechanics or rules. Those are not copyrightable, and while it is ethically questionable, there's nothing illegal about copying mechanics completely while putting a new skin onto the game.
It's less valid if it's copying art or sound assets. Unfortunately, this discussion isn't about mechanics(as tbaltree notes in the thread), it's about the specific art assets.
He's claiming that they didn't copy the assets but inspired themselves from them. He's claiming that they (just like everyone else) are building upon the shoulders of giants.
That argument is perfectly valid, until the accusing party pulls your files named after their own bosses (carrying the typos along too). At that point, you've pretty much been proven wrong.