The CSV format (Comma-Separated Values) is a plain-text format to exchange spreadsheet data. It can usually be imported and exported by any spreadsheet application such as LibreOffice or Microsoft Excel. Reading and writing to csv format is done with python's built-in csv module.
Importing a .csv file into FreeCAD creates a spreadsheet object, then fills it with the values from the file.
Exporting a spreadsheet object to a .csv file simply writes all the values of the spreadsheet object. Functions, such as "=A3+B5" are written as functions, not resulting values.