This is a feature of Excel that allows you to open the same workbook in multiple windows. To do this on the View tab, select New Window. Each time you do this, the file name will have a number added to the end in the title bar. Saving a workbook with multiple windows open will result in all the windows opening the next time you open the file.
To have only one window for the file open the next time, first, close all the windows but one and then save the file.