First and foremost I would advise you to relax. Diabetics especially children sometimes can have sensitive bladder. Because of this even small amount of urine in the bladder can give an urge to urinate. This will pass with time. As long as he can hold the urine, it wouldn't be much of a problem. However if he starts urinating without knowledge then we need to deal with the issue. You can meet the pyschologist but I dont think it would be much helpful. My advise is to have him checked for UTI again after a month or so, otherwise dont worry about it.
Hope this helps
Dr. Om Lakhani
http://www.healthcaremagic.com/doctors/dr-om-lakhani/60313 (online expert diabetes