The testicle is suspended by spermatic cord
which enters the scrotum
through groin from stomach.This cord contains muscle called cremaster which contracts sometimes.
So,due to the contraction of the muscle during lifting,your husbands testis is changing its position.
If there is no swelling visible or palpable,then it is not of much concern.If there is swelling in the groin which is disappearing in lying down posture,it could be hernia
It is natural.
If you still have doubt,consult a surgeon and get an ultrasound
Wish him good health