The university was placed on lockdown for several hours, as police officers with weapons drawn canvassed the campus.
ECU officials sent out alerts to faculty, staff and students around 10 a.m. after getting two 911 calls reporting the suspicious man.
They looked at surveillance video on a busy thoroughfare through the heart of campus, and spotted a man with what appeared to be a gun sticking out of a backpack.
After an intense search, the Greenville Police Department caught up with the man and learned he didn't have a weapon - it was an umbrella.
Authorities said rumors spreading on social media sites created great obstacles for police, causing them to "chase ghosts."
"Through Facebook and Twitter, things started to develop. Obviously, a bunch of rumors were going around. So honestly, I think people on campus didn't know what to believe," said student Matt Edward.
"When you do things that cause fictitious information to go out, it hinders the actual efforts of police agency. It actually delays us, and that's finding the person we're looking for," said Sgt. Carlton Williams with the Greenville Police Department.
ECU Chancellor Steve Ballard said in a statement Wednesday that the university was "relieved that the reports of this incident turned out to be unfounded."
"East Carolina University will always err on the side of campus safety when these situations arise," Ballard went on to say in the statement. "Our response by faculty, staff, and students was timely and professional. We appreciate the concern of the parents of our students, as well as the cooperative efforts of the Greenville Police Department and the Pitt County Sherriff's Office as the university responded to this incident."
Greenville is about 85 miles east of Raleigh.