The data... oh heck I will look something up for you... Here you go.

Roughness. If the surface is rough at the scale of the radio wavelength (that is, if it is blocky or pebbly with block sizes of one to a few centimeters), then the facets of the blocks that are oriented perpendicular to the radio beam will reflect the signal like myriad little mirrors, making the surface appear bright.

This brings up an important point that I did not mention, that pretty much every observation you make with a RADAR instrument has to be interpreted with the wavelength of that instrument in mind. The linked piece does a really good job of explaining that when it compares Cassini RADAR with Magellan and space shuttle.

You also mentioned your seeing other data that the project scientists have access to. Depending on the instrument, it is probably not in an image format that you can look at and make sense of. The RADAR data for instance is put together into an image, which you saw with the news story. It is also put through various analytical seives and comes up with tables of numbers that you and I could make no sense of whatsoever. If you really have an interest in seeing all the data, then you should get yourself a PHD in the field and go for it. Till then, if a scientist says his RADAR instrument indicates a very smooth surface, then you should probably believe him.