Hi eric, Michael T has explained it well!

Just in case here is a visual to additionally clarify it - the dimensions being displayed for your squiggly curve are the width and height of its bounding box, shown here selected:



But for lines the length of the line is shown and not its bounding box - you'll see the dimension labeled as "Size" for the bounding box readout, but instead the label in front of the dimensions will read "Length" when a line is selected.

- Michael