Passing the range is optional, as per the documentation. However, when used with a separate range parameter, it does return correct results. Note that specifying a range inside the text prompt will not work, even though it should be the exact same request sent to the model.

I'm not sure what the intended purpose for this is, but it can return crazy numbers when doing math. You can ask it to add some cells in a completely empty spreadsheet and it'll return some random numbers.