this happens when an image is rescaled. Your original images is 1600px wide and is being rescaled to 900px. So the image is at 56% of its original size. Should improve if the original was 1800px, so the rescale is exactly 50%.
Did you change the name of the new image file before uploading? As its still displaying a max 1600px image size. Changing the name will ensure the correct file is being used ( its a WordPress annoyance ).
Just so as you know this is how the current image looks on my Mac.