That's not what happened. A quote from the letter said
"We want to emphasize that we do not know if the emails, provided to the New York Post by President Trump's personal attorney Rudy Giuliani, are genuine or not and that we do not have evidence of Russian involvement—just that our experience makes us deeply suspicious that the Russian government played a significant role in this case."
The laptop did have all the classic characteristics of Russian disinformation. That is undeniable and is exactly what the letter said.
en.wikipedia.org