3D-printing ranges from fragile resin pieces to metal durable enough to use as rocket nozzles. This article was about 3D printed titanium, so the resulting piece is likely stronger than bone but weaker than machined titanium would be.

It is most likely made of welded titanium particles as others point out.

Imagine a thin layer of titanium dust. Then shine a laser on the points where you want to weld. When done, add another layer over it and repeat.

Or imagine a nozzle which sprays titanium dust. Directly after the nozzle there is a focused laser point. When the dust goes through the laser it welds together. So when you do this close to a titanium surface you can add more titanium to it.

And there are other methods for 3D printing metal. But most of them are just advanced welding techniques.

3D printing metal is usually done by sintering a metal powder. The technology is good enough for turbine blades in aircraft engines.

It's made of titanium (though almost certainly some alloy) so they probably used a DMLS (direct metal laser sintering), SLM (selective laser melting) or DMLM (direct metal laser melting) process. All will result in fairly strong material structure. Probably not as strong as tempering/quenching would make it though. Either way, this is not something you can do with a hobby 3D printer :-)

The article says it’s titanium

This is just “manufacturing” which has little resemblance to the consumer makerbot products