the pilot holes for the M4 bolts are inboard of the end of the wing tube so they don't appear to be intended as a stop for the wing tubes.
the only purpose I could see for them was too keep the wing from sliding out off the wing tube in the event of a failure of the 1/4 by 20 nylon bolts.
If there is an other purpose I would love to know.
As an added thought the wing struts would also aid in retaining a wing in case of a failure of the nylon bolts truly seams overkill to put in those ugly bolts down threw the wing.