It is simply confusing .
What they intend to say is that as speed increases - the wing(s) will generate more lift- pretty std stuff
So at faster speeds - to keep from needing to reset tail plane angles - reduce positive wing angles .
In my book -for models such as this - the wings all should be fully symmetrical- and set at zero -zero
For THIS type plane, the airfoil used is of very little -if any importance as long as it is thin, strong , stiff and accurate.
So make sure your model checks out -use a stick marked to check assembled measurements and make left/right sides the same - use solid control links and acurate servos.
Then trim for your favorite flying speed by shifting CG and tail plane incidence .