Yeah, those kinda puzzled me as well. They didn't look like they're varnished, but I suspect I could be wrong about that. After all, they do work, lol đ.
It works for now, but the reason most wires have a rubber-like insulator around them is that it takes very little to Crack or abrade a thin coating such as this and turn it into a fire hazard.
I'm surprised a product with such a small safety margin is allowed for sale.
I once accidentaly shorted the connector cables of a battery pack with 4 AA batteries. It very quickly generated enough heat to set the insulation of the cable on fire.