Historians pull their information from sources of all kinds. For example, a piece of propaganda from WW2 (which is likely to be almost completely untrue) could be an invaluable insight into determining a collective mindset of the time. Similarly, a diary of someone on the street, who's been taken in by that propaganda is also useful.

Adam Curtis exists in the outskirts of a behemoth of a broadcaster, so his interpretation of these events will be useful - especially given that they are broadcast so widely.

You think that current historians only look at stuff that's true to get an insight into the past? Can you spot the flaw there?

How can any one individual get an insight into a population of millions -- without making at least some concessions to practicality, and the generalisation and other "technical" untruths that this implies.