No doubt it is complicated. Not a lot of historical evidence.
I don’t know much about the lecturer. I am not saying he’s wrong on anything but I do believe he could have presented some things better. He also states that he was a bit under the weather at the time of his presentation so I’ll cut him some slack. He knows a lot more about that time frame than I do.
A quick search of 'Depths of Pentecost' yields - http://www.depthsofpentecost.com/index.html/. There is found an article by Philip Cottraux - Brother Philip is an assistant teacher at his church in China Grove, North Carolina. I agree his presentation lacks academic authority, which can be a good thing or a bad thing, depending. Given the somewhat limited society of Scroll scholars, it is obvious that he is a teacher of the less informed...
Still, as I said before, I do not wish to take issue with his presentation in general. Given the controversies arising surrounding the scrolls - and historical Israel in general - he is probably just being cautiously conservative. The emergence of academic 'Minimalists' - who pick at all sorts of historical details about Israel - has thrown the whole subject into disarray.