Darnell Rodgers, 18, was walking up to another floor when the stairway suddenly became flooded with students.
"They were screaming, and they were saying, `Oh my God! Oh my God!' I knew something was wrong, but thought that it was probably just a fight, so I just kept going," Rodgers said.
He realized he had been shot when he felt his arm burning.
Rodgers was released from a hospital after treatment for a graze wound to his right elbow. He told NBC's "Today" on Thursday that he didn't believe he was targeted and that the shooter didn't speak as he fired.
"He just fired the gun," Rodgers said. "He didn't say anything."
The other student shot was taken to a children's hospital, which would not release the student's condition.
Michael Grassie, a 42-year-old history teacher, was hospitalized in fair condition late Wednesday after about 90 minutes of surgery. Without naming Grassie, emergency room physician Thomas Collins told "Today" that the teacher who underwent surgery had sustained "some pretty significant injuries" to his spleen and pancreas, "but he's a very tough man."
SuccessTech Academy, with about 240 students, is an alternative high school in the public school district that stresses technology and entrepreneurship.
Associated Press writers James Hannah, Terry Kinney, M.R. Kropko, John Seewer and Thomas J. Sheeran and Andrew Welsh-Huggins contributed to this report.