The thing is, Islam emerged in literate times. Historians were writing journals. Scholars were writing diaries and letters. Jurists were writing bureaucratic articles. So from the 7th century onward there was a rich record of documents, and that's why we know so many historical details.

Noooooooooooooooooo...

Noooooooooooooooooooooooooooooooooo!

Ok I'm done having a minor aneurysm. But yeah this is a wildly inaccurate statement. It massively overstates the reliability of the documents he's apparently working from (I.e. Ibn Ishaq via Tabari and Ibn Hisham), is apparently ignorant of how that information got passed down (I.e orally, not written down) and fails to mention how poorly documented the 7th-8th centuries are.

/u/Shlin28 gives a great description of just how poorly documented the rise of Islam is on the Christian side here: https://www.reddit.com/r/AskHistorians/comments/3yencp/how_did_christians_react_to_losing_so_many/cyd28pl

I've written quite a bit on the historiographical controversy over the use of these "traditional" sources, for instance here: https://m.reddit.com/r/AskHistorians/comments/3pm6tg/what_are_the_most_reliable_sources_on_muhammad/

I only listened to the first ten minutes or so of this YouTube video, but even accounting for the fact that he's uncritically relying on this dubious traditional sources I heard a good bit of bad history. A shura council is not "like a democracy", for instance.

Some effects of the unreliability of those sources as it pertains to the video:

We cannot reliably quite Muhammad.

We cannot reliably say who was or was not present at battles.

We cannot reliably say how many people attended a speech.

And so on. There are people who defend the use of traditional sources, and they are of course a matter of faith to Muslims. Its an incredibly contentious issue. Personally I'm not willing to reject their content entirely but find any specific details to be incredibly dubious.

As I mentioned in the other post Robert Hoyland's Writing the Biography of the Prophet Muhammad: Problems and Solutions is a great essay-length overview of these issues and available as a free PDF if you do a search for it.