Are you saying that they didn't let him shave his beard.....But they let him shave his mustache?
Some guys don't have a lot of natural upper-lip hair, 'specially when young. I remember in high school and college, a few of my friends got thick beards fairly young but only very wispy upper lip hair until later -- the reverse of the more usual pattern where the moustache grows in first.
I have a hard time believing that a Muslim would shave the moustache but not the beard -- they all seem to prefer full facial hair, or moustache only. Shaving the upper lip but letting the beard grow is an Amish custom.