No, the matrix keypad does not work with voltage dividing principle. It instead works with columns touching rows. With a regular matrix keypad, where 123 are one row one, and 147 are on column 1, pressing 1 connects row 1 with column 1. If your column 1 is at GND and you sense row 1, you find row 1 to be LOW. If there is no pushing, then column 1 and row 1 are not connected so then row 1 will not read LOW (internally pulled to HIGH) and read HIGH. So the keypad library scans all columns and rows to determine which keys are pressed. Did that help?