Assets are a special type of Field with additional functionality. Where possible to try to detect the type of file upload and return an appropriate Field. Image classes are returned when the file has one of the following extensions: ‘.jpg’, ‘.jpeg’, ‘.png’, ‘.gif’, ‘.webp’. See the Image documentation for more.
To check if a file has been uploaded in Storyblok call hasFile() on the Asset.
$myAsset->hasFile();{info} When using multi-asset fields we only receive a URL from Storyblok the Asset|Image fields are less complete.