Yes and no.
He has to report the capital gain, if it was more than $10,300* (a single person's filing threshold). If the gain was less than $47,750, and is a long term gain, he will not pay any tax as long term capital gains (LTCG) are taxed at 0% for people in the lower tax brackets.
* The numbers are different for people who can be claimed as a dependent by someone else. The filing threshold is $1050 and tax will be due on a LTGC greater than $38,500.
Those numbers assume you have no other reportable income.
