He may have what is called a "retractile testis" on the right side. Here, while the testis made it to the scrotum, the gubernaculum (the "anchor" that keeps the testis in the
scrotalGenital injury
Scrotal mass
Scrotal masses
Scrotal swelling
Testicle ultrasound sac) may be stretched or otherwise ineffective. The main risk is that this could become what is called an "ascending testis" where the testis essentially acts like an undescended testis--it stays up in the canal. Having one undescended testicle (the left) may have incresed his risk of having an abnormality of descent on the other (right) side.
Your pediatric urologist can help with this (and it is ok to wait until the appointment). The repair (if needed) will be the same as that for the Left side. Perhaps he will give you a two-for-one coupon!