Why does Calc print out all the worksheets in the spreadsheet?
By default, Calc is configured to do just that. But changing this action so that it performs that only the current sheet is printed is as simple as going to File -> Print -> Options and then ticking the Print only selected sheets for Document. To make the change permanent for all occurances of OOo Calc, go to Tools -> Options -> Spreadsheet -> Print and select the same option: Print only selected sheets for Document.