What was happening was this: in its pure state of repeating units of one titanium and two oxygen atoms, titanium dioxide is a semiconductor. Heat the material, though, and some of the oxygen is driven out of the structure, leaving electrically charged bubbles that make the material behave like a metal.
The memristor they've created depends on the movement of oxygen atoms to produce the memristor-like electrical behavior. Purely electrical components such as resistors, capacitors, inductors, and transistors only rely on the movement of electrons and holes to produce their electrical behavior. Why is this important? The chemical memristor is an order of magnitude slower than the theoretical electrical equivalent, which no one has been able to invent yet.
I think the memristor they've created is a great piece of technology and will certainly prove useful. However, it is like calling a rechargeable chemical battery a capacitor. While both are useful things, only one is fast enough for high speed electronics design for applications like the RAM they mentioned. On the other hand, a chemical memristor could be a flash memory killer if they can get the cost down (which I doubt to happen any time soon).