I've not made a lot of mittens and never seen that direction but I have an idea. Sometimes when you are working on dps when you are doing something that may create a gap I have knit into the back of the first stitch where the gap might be and that closes it. Maybe this is similar to that. It sounds like it is saying to make a twist right there on each side of the gusset. On the next two stitches to knit the 2nd stitch and then knit the 1st stitch. At the other side it would probably be 2 stitches before the gap--stop and knit the last stitch and the next to the last stitch. It would be like a mini cable twist.
What do you (or anyone) think? Does this make sense? You might try it and see it is works. You can always rip it out if it was crazy. LOL That's the good thing about knitting....you almost always have a second chance.