One possibility is that this is the result of the cremasteric
reflexBabinski's reflex
Infantile reflexes
Moro reflex
Urge incontinence. The normal response in males is a contraction of the cremasteric muscle that pulls up the scrotum and testis on the side stroked, sometime leading to retraction of the testicle.
A hernia can also cause this symptom, and this should be evaluated by a urologist.
Regarding the shrunken testicle, I would suggest a scrotal ultrasound to evaluate whether the blood flow to the testicle or if the testicle itself has any abnormality causing any abnormal size.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Thanks,
Kevin, M.D.