It might teach you about what tools he uses, and what keyboard shortcuts he likes, but not about the more important tasks of understanding problems, and organising solutions. That's what makes writing software hard, not the "coding" part.
Also, as the article suggests, the developers appear to describe what they're doing, so it could be a window into the thought process of a talented developer. I think I would have valued this quite a bit as a novice when the technology to enable this wasn't as developed.
It can also help if the solo programmer is "rubber ducky" programming[1], but people typically assume more shared knowledge than actually exists. It takes another human to counteract this by asking for clarification.
Edit: I don't get how HN footnotes work... So I'll just pretend this is close enough.
For example, I watched the linked video. Using it as an example for Python programming would be terrible - it does not follow PEP8 (extremely long lines, no spaces around operators, excessive descriptive names ("Java style")), has many unnecessary assignments and copies, very few comments, no sphinx docstrings, etc...
Where do you go to learn the proper way to do that? Couldn't you teach that through streaming as well?
Even if the viewer isn't learning much, the streamer certainly might be because he's getting people to review and help him. Maybe the real value is in what the streamer can learn, and not really the viewers.