Unless the ethernet cable is made from copper clad steel, which is sometimes used for ethernet cables and very common for consumer grade phone and RF cables.
It's actually pretty cool - it's very flexible and convenient.
It's difficult to solder and impossible to crimp though (so we use these factory-made), and I would not use PoE with it (the gauge - 32AWG - also means that it is really thin, and as it's steel, the resistance must be terrible. But for data, it works good.)