Even in my usage of butler, I've actually never seen an image like that while editing a game. o.O Perhaps because I haven't done web uploads with it? To be honest I find your confusion with the channel names mystifying because it was obvious to me, but if one person has difficulty with it, there's likely to be more, so I agree the docs should be modified.
As for the error you encountered, you really should point that out to the Itch.io team because that's probably something they need to look into. Glad it's fixed for you now though. ^^