Your featured image on this page.
Is being loaded from JetPack plugin’s server.
This is your image url.
Go to your JetPack plugin settings to disable Photon Module.
And it will use back theme generated featured image.
By the way, from the theme codes I can see the post thumbnail size is
add_image_size('post-thumbnail', 680, 330, true);
This means your image will be cropped to 680 x 330 or less, depending on your uploaded image aspect ratio.
I suggest you to try and resize your image to 680 x 330 before uploading in order to avoid much cropping.