Well, there are3 reasons that 7megapixel would not be different to 5.
1) At the print size you have chosen, the human eye cannot perceive the difference. I think you need to print about A3 for 7megapixel. Remember that 3.5Megapixel is more than fine for A4 print.
2) The image you have chosen is already fully resolved at 5megapixels and there is no more detail to see. You could try a test of something with many fine lines in it to see.
3) The lens is not of a suitable quality and therefore does not allow the sensor to make use of its resolution.
I would have thought Casio would have chosen a suitable lens glass quality that would be able to show the difference. Afterall, they chose a lens with more elements in this camera than the Z57 (based on Pentax lens).