Yeah, there is a slight discrepancy between the preview and the cooked image.
In the preview, we’ll always show the original image resized to fit the “{max image width}x{max image height}” (690x500 by default) dimension.
In the cooked post, we’ll often show the optimized image which might get cropped if it’s taller than 18:9 (latest phablets form factor).
That’s what’s happening in your case. The image ratio is 3212 / 1064 = 3 which is taller than 18 / 9 = 2.