The color blocks in this tool, being evenly-colored, provide a worst case scenario for noise levels. The samples provided for the Rebel T6 have no noise reduction applied, a key piece of information. Noise reduction can be applied in-camera (it is applied by default) or via software during post processing. The downside is that some detail is generally sacrificed with noise reduction application. The site's standard color block samples show what the camera is capable of without noise reduction.
As mentioned, in-camera noise reduction is always available in EOS DSLRs, and noise reduction is also available during post processing. Noise reduction is very effective at reducing visible noise, but it is also destructive to the details in your image and to image sharpness. Even at ISO 100, the standard out-of-the-box noise reduction will have an effect on your image quality. I usually apply light NR only to my very high ISO images.
How does Noise Reduction work in this camera? As far as I know its done by taking ten photos and blending them together.