The dispute took place yesterday afternoon on campus.
While the man did not have gun, police say they initially suspected he could have been armed.
Authorities arrested the man Tuesday.
They say he came to visit his ex-girlfriend who is an ISU student.
She called police reporting he had a gun and displayed it to her.
But after interviewing both parties, officers discovered he only implied he had a gun.
The initial report put ISU on high alert, and placed parts of the campus on temporary lock down.
Charges have yet to be filed against the man.