By default, All in One SEO Pack outputs images in the XML Sitemap to comply with search engines such as Google that want images submitted to them for indexing in Google Images. This feature was added in version 2.4 of the free plugin and version 2.5 of All in One SEO Pack Pro.
You can disable this feature by using the filter below:
add_filter( 'aioseo_include_images_in_sitemap', '__return_false' );
Filter added in All in One SEO Pack v2.4 and All in One SEO Pack Pro v2.5.
Note: while this filter can be used conditionally, for example when detecting a Yandex bot, you can alternatively just use the option to exclude images from All in One SEO.