If you look closely you can see the the TE of the inboard section actually has some sweep, outboard of the wing struts the TE is straight.
The reasoning for making the root LE sharper then the tip LE is to help promote the inboard section of the wing to stall before the tips. The theory is that the airplane will stall more predictable and with more control. When I designed my Divergent pattern airplane I used this technique not only on the wings but the stabs as well. The feature was designed into the airfoils. Another feature I used was the airfoil percentage thickness was actually increased from root to tip. It's a double taper wing so at half span the cord was reduced by 1.75" but thickness remained the same, at the tip the cord is 6.5" which is 50% of the root cord but looses only 35% thickness. The TE of the wing is fairly sharp at the root as well but 3/16" thick at the tip. The end result is an airplane that is extremely predictable and must be forced to stall. In fact both snap rolls and spin entries are now flown through with virtually no stall presence.