All media have the option for alternate text, but only images and uploaded videos have the option to add attribution. Audio files, uploaded or linked, do not have an attribution property. Linked videos (such as from YouTube), likewise do not have an attribution property (presumably because one can click on it and go to the original video).
We stress the importance of citing sources and attribution properly to students; having a consistent format to add attribution to all media types (and if possible, to have it integrate with attribution options for text), would help. While one can workaround say, attribution issues with audio by adding a detailed caption, it would limit confusion and just make sense to have consistent attribution properties across all media types.
For fun, here's a demo storymap I made noting the attribution options for various media across different StoryMap block types: https://storymaps.arcgis.com/stories/0c6d797c5ea64e39972c7ef88b7c8500
