At the moment, Stream does not support audio-only uploads.
The documentation page to which you refer is listing the audio codecs supported within a video container. I understand that this is a bit confusing, and will work to make this restriction stated a little more clearly.
If you would like to upload audio files to Stream, currently the only approach is to create a blank/static video with your audio file as the contained audio track. The folks over at Youtube have great instructions on how to convert an audio file on both Windows and Mac here