Not just the title, but the article itself. "New research, using ultrasound, has developed an invisible 3D haptic shape that can be seen and felt."
Visually, the researchers have demonstrated the ultrasound patterns by directing the device at a thin layer of oil so that the depressions in the surface can be seen as spots when lit by a lamp.
They were probably referring to the oil depressions being visible but the title is certainly misleading.