Page From Grade A becomes Grade C

hi, i have tried out your flying images plugin and tested it with GTmetrix, I saw the images have been compressed because I set to 80% deduction but I did not know why and how the cdn.statically.io from? it makes the image waiting/loading time becomes slower and longer, therefore my site before installing flying images score is grade A but after installing and activating your plugin, it becomes grade C.
btw, i did not see the images change to webp format?

kindly assist, Thanks