Mica is a good insulator. It has been used for a long time to insulate TO-3 and TO-220 package components (transistors, regulators, amps) from their metal heatsinks or chassis. It has been used in electronics, but in the opposite sense of what this video is implying.
Bare nichrome heating elements (like from hair dryers) often use mica as well to insulate the heating wire electrically and also to withstand the high temperatures. Again, this is the opposite of what one would want from a circuit.
The video isn't implying anything other than the narrator thinks it's a "circuit," which is nothing but clickbait. Mica can be used as a high voltage dielectric in capacitors, so the capacitor is a simple circuit, albeit a useless one without more parts. I'm sure there are trace amounts of copper, gold, silver, and silica in there as well, none of those mean anything either. It's even possible that there is some quartz that was placed next to a piece of mica and it made a crystal that could oscillate.
My point is that, while the mica could be a part of something greater, the presence of mica doesn't mean anything other than they used rocks, which can often contain traces of mica.
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