treabba Hi
There is no place to add image for this open graph tag for the homepage of your site so at this moment, it takes the first image in the gallery section as the image when sharing into social sites.
You can go to the home menu item of your site and add an image via Link Type and see how it goes:
Also add this custom css to hide it from the main menu on frontend:
.t3-megamenu .nav > li > a > img {
display: none;
}