I agree with you. There's nothing "4D" about this process. In fact, it seems to be only a 'process' of 'printing a certain type of material in the correct places so that the printed object will react in a prescribed way when placed in water (or some other liquid or gas or even an oven?). The 'printed' item still has just the three dimensions of length, width and depth, as far as I can see. I've usually heard of 'time' (or 'space-time') as being the accepted fourth dimension but other phenomena could be used, ie; color, odor, temperature, magnetism, electrical charge, etc.
If the demo is what the author (or MIT) calls 4D, they need look no farther than a potter or even Henry Ford to see things changed from one shape to another... right before your eyes! And no water tanks required!
OTOH, maybe they are using 'time' as their meaning of a fourth 'dimension.' Can I then say that my body is an example of the fourth 'dimension?' It certainly has changed... over time!