The circuit in the picture is a chaotic generator formed from MOSFETs as opposed to op amps from the usual chaos generators.
How does it all work exactly? Whilst I have knowledge of how MOSFETs work and such, the connections etc are hard to understand what they all do completely.

In-depth theory of this would be greatly appreciated.

 

Each pair of MOSFETs is an inverter as in the 4069UB.
That should help you figure it out.
But . . . .
It looks to me like a Pierce LC oscillator with a few extra connection blobs that shouldn’t be there, and he position of the earth connection looks dodgy.