In your case, that completely depends on whether his college considered him a full-time student in 2016.
IRS Pub 970 isn't 100% clear on what constitutes a "full-time student" other than to say it's up the the school:
A student was enrolled at
least half-time if the student was taking at least half the
normal full-time work load for his or her course of study.
The standard for what is half of the normal full-time
work load is determined by each eligible educational institution.
However, the standard may not be lower than any
of those established by the U.S. Department of Education
under the Higher Education Act of 1965.
It seems unlikely that the IRS would complain about his full-time status or claiming him as a dependent.
In your case, that completely depends on whether his college considered him a full-time student in 2016.
IRS Pub 970 isn't 100% clear on what constitutes a "full-time student" other than to say it's up the the school:
A student was enrolled at
least half-time if the student was taking at least half the
normal full-time work load for his or her course of study.
The standard for what is half of the normal full-time
work load is determined by each eligible educational institution.
However, the standard may not be lower than any
of those established by the U.S. Department of Education
under the Higher Education Act of 1965.
It seems unlikely that the IRS would complain about his full-time status or claiming him as a dependent.