Your interpretation of what the Pentagon said does not match the quote. They are very careful: they cannot definitively conclude that the video includes the uses of cluster munitions. That’s not to say that the video doesn’t show cluster munitions or that Russia isn’t using them elsewhere.

The second link does conclude that Russia has used cluster munitions. That is with the benefit of over a year to gather evidence.

From your link:

Ukrainian forces have used cluster munitions that caused deaths and serious injuries to civilians. Russian forces have extensively used cluster munitions, causing many civilian deaths and serious injuries.

Here is Pentagon again as of July 6, 2023: Brigadier General Pat Ryder: “I would note that the Russians have already been employing cluster munitions on the battlefield, many with very – which included very high dud rate reportedly.”

Also cluster munitions used by Russia

I wouldn’t be surprised if both sides have been using them.