He didn't make the old COVENANT with their fathers and that's what being referenced here. The COVENANT. But as the article demonstrates, there is ample evidence that the violation of the laws as codified by the ten commandments were sins before the covenant was ratified.
Let’s read it again.
5:1 ¶ And Moses called all Israel, and said unto them, Hear, O Israel, the statutes and judgments which I speak in your ears this day, that ye may learn them, and keep, and do them.
Deu 5:2 The LORD our God made a covenant with us in Horeb.
Deu 5:3 The LORD made not this covenant with our fathers, but with us, [even] us, who [are] all of us here alive this day.
He then begins to list the Ten Commandments.