"to the gather" just means the pleats do not all match in appearance or size and are more "ruffely".

In a tailored kilt, pleated to the set or stripe, every pleat will contain the exact same pattern. Like in this photo, the pleat is to the red stripe (vertical stripe) and the waist band lays flat against the waist.



On an SK, the pleats might contain a blue stripe and then a green stripe or a brown stripe or maybe part of both and the waist band would be bunched together with the elastic and appear more billowy or puffy. Sorry I don't have a photo of the back of my SK but since you own one you'll be able to see what I'm talking about. Since the pleats are not sewn in, over time the kilt will require serious ironing to keep the pleats right and will also have to be adjusted individually to get an appearance similar to the photo above. I did this a few times trying to keep it pleated (and ironing is therapeutic to me since my military days) but I just got tired of having to adjust the pleats every time and then still have the puffy waist band in the back.

To be clear, I love my SK for lounging around the house. I don't have another kilt that is better for crashing on the couch in, but when I want to strike a crisp clean image, I'll go with one of my kilts with sewn down pleats.