Harpreet Gill, 36, a senior manager with the e-commerce retailer, was shot dead during a confrontation with the suspects in the Bhajanpura area of the capital late on Tuesday, police said.
Mr Gill's uncle, shop owner Govind Singh, was also shot. He is receiving hospital treatment.
Police on Thursday arrested an 18-year-old man, identified as Bilal Gani, and accused him and his associates of slapping Mr Gill and his uncle after their motorbike and a scooter made contact as they passed each other.
The police said the accused then shot Mr Gill in the head and Mr Singh in the face.
Deputy Commissioner of Police Joy Tirkey said the bullet entered from the right side of Mr Gill's head and exited from the other side.
Efforts to track down and arrest the four other suspects are continuing, police said.
Incidents of road rage are common in Delhi. With 22 million residents and 13.4 million registered vehicles, the city's roads are congested so traffic jams, and angry encounters between drivers, occur frequently.
On Monday, a man was killed after he reportedly intervened in a fight between three people and a taxi driver. In April, a 39-year-old delivery worker was allegedly beaten to death by two men for not giving way to their car.
Although there is no recent data on road-rage incidents in the city, 222 cases were reported between 2015 and 2017, according to Hansraj Gangaram Ahir, the former junior minister of home affairs.
Mr Ahir told parliament in 2018 that 92 cases of road rage were reported in 2015, in which four people lost their lives and 80 were injured; two people were killed and 55 injured in 66 cases reported in 2016; and three people were killed and 55 injured in 64 cases in 2017.