There are no values from the spreadsheet in this case. "The numbers above" are just text to the LLM.
They could of course require that optional cell or cell range parameter after the prompt, but that would eliminate some use cases. "Generate some text", one of the stated use cases in the help text, doesn't reference any cells.
Also, numbers in Excel aren't necessarily as clear cut as you make it seem. Excel famously thinks everything is a date, and how number-y must a number be before it isn't okay?
Not to mention there are other things to do with numbers which don't require arithmetic. What if someone wants to have Excel translate 34 to "thirty-four"? Or have Excel generate a poem 34 words long? Or whatever else nonsense people might try.