Luby told CNN that he was having a drink and smoking on the patio when a manager asked the man to leave. A bar regular, Ian Grillot, stepped in to help escort the man out.
"He said (to Grillot), 'Why are you standing up for them?' He emphasized 'them,' as if them was a derogatory term," Luby said by phone from Olathe, Kansas.
The man, who police later identified as Adam W. Purinton, went out to the parking lot and stumbled around for a while, then got in a pickup and left, Luby said.
Luby, 41, went back inside the restaurant and told the bartender he wanted to pay for the Indian men's tab "as a way to help," he said.
When Srinivas Kuchibhotla and Alok Madasani found out Luby had picked up their tab, Kuchibhotla walked over to thank him.
"Srinivas came over and introduced himself. He said, 'Thank you.' I talked to him for a few minutes," said Luby. "I was just talking to him about what they did for a living."
They shared a common bond. Both worked in the tech industry. Kuchibhotla was an engineer at Garmin; Luby is a computer programmer.
Luby went back inside to go to the bathroom. As he was headed back outside he heard a loud, "Pop! Pop! Pop!"
"There were a lot of screams," he said. "From where I was, I didn't have a view of what was going on. People started running our way. Then I ran into the manager's office."
A terrible thought crossed his mind.
"(Crap), he came back," Luby said, thinking of the suspect. "It was a few minutes or so. Time is a blur. I went outside. People were screaming."
Outside, Luby saw Grillot laying on the ground. He had been shot.
Grillot was surrounded by people trying to help. Luby said he took a first-aid kit out of his car and got gauze to stop the blood spilling from a chest wound.
Almost 24 hours later, Luby was back at the scene, struggling with his emotions and recollections.
"I'm tired, I'm hungry but I can't eat. I'm going on autopilot," he said. "I just came back to the restaurant to walk."
Luby told CNN there was something different about the suspect.
"He was wearing a white shirt with fake military medals, like those Captain Obvious commercials. I don't know, but the guy was different. I've never seen anyone wear a shirt like that," he said.
Purinton has been charged with one count of premeditated first-degree murder and two counts of attempted premeditated first-degree murder.
Luby plans to attend a service Friday night at a church across from the shootings scene.