Just a thought. If you sons urine was tested for an infection, it may not have been tested for sugar level.
And, as has been pointed out, many T2's are not overweight, or eat rubbish, or dont exercise. Sometimes its genetic, or just the way it is. The media have focussed on overweight type 2's and ignored the many type 2's who are slim, eat healthily and exercise. So keeping an eye on your family blood sugar levels is a good idea no matter how slim, healthy and active you all are.
In my family we have 3 generations of type 2's, all different weights, lifestyles and exercise plans, but all diagnosed around our mid 40's.