Also, the preamble does not say that all 17 highlighted cells need to be contiguous. And because of symmetry, there must be an odd number of cells on the axis
Without trying to give the whole thing away on here, look for 13 linked letters which satisfy both the description SEA and the letter C. So the shape is relevant
For what it's worth, novice, I agree with you. I spent longer looking for the highlighting than I did filling the grid, and that's far from unique for me. I stopped doing the Listener for a while for that reason, and may well do again soon