Possibly a vocabulary mismatch.
In Numbers:
Spreadsheet means the whole document.
A Spreadsheet may contain one or more Sheets
A Sheet is a 'blank canvas' extending as far as necessary down and right from the top left corner of the workspace. In Numbers 3, Sheets are often referred to as Tabs, due the series of Tabs across the top of a Numbers 3 workspace showing the names of the sheets in the document.
Each Sheet may contain one or more Tables, (plus other objects including images or other graphics, text boxes and charts (graphs)). These objects are placed 'on' the sheet.
A Sheet is NOT a large grid of cells. It is, as noted above, a blank canvas on which objects (including Tables) can be placed.
A Table is a block of cells arranged in rows and columns. Each Table is independent of the others on the same sheet. Adding or removing rows or columns from one table does not change any other Table on the Sheet. Changing the row height of one or more rows in one table has no effect on rows in the other tables on the same sheet.
Regards,
Barry