I don't know exact meaning yet, but it looks that this is additional info for the Flash API about the shape. This info is not needed and you can delete this lines and still load the XFL without problems. The cubics data will be added again when you try to edit the shape again. It's just something like a cache info.
You can see it here:
<Edge fillStyle1="1" strokeStyle="1" edges="!2720 2720|0 2720!0 2720|0 0!0 0/2720 2720"/>
<Edge cubics="!0 2720(;0,2720 0,0 0,0q0 2720 0 0);"/>
<Edge cubics="!2720 2720(;2720,2720 0,2720 0,2720q2720 2720 0 2720);"/>
<Edge cubics="!0 0(;0,0 2720,2720 2720,2720q0 0 2720 2720);"/>
This is triangle consisting with 3 lines and the related additional cubics info.
Also note that the edges data is unnecessarily verbose. The same shape could be described like:
ChangeStyle:
Move: [2720 2720]
FillStyle1: 1
LineStyle: 1
Line: -2720 0 0 -2720 2720 2720
This one is for two lines, one horizontal and one vertical:
<Edge strokeStyle="1" edges="!2640 3020|2640 5240!1520 1740|4879 1740"/>
<Edge cubics="!1520 1740(;1520,1740 4879,1740 4879,1740q1520 1740 4879 1740);"/>
The data does not change with each shape change so it must be just some internal helpful stuff. I recommend to remove these lines if you want to build/modify the shape data with some external tool (as I want to do).
Fenomas is right that the numbers are in twips so if you want pixel values, you must divide them by 20.