The 28-year-old had been involved in the youth-led protests that have upended Kenya since last month and had been released by police only hours earlier following his arrest at one of the demonstrations.
He shouted for help.
"But people were also running. So they took me," he told Reuters.
Dozens of Kenyans have been targeted in similar abductions in the past two weeks, said human rights groups, who blame the extrajudicial arrests on Kenya's intelligence services.
Organized online and leaderless, the protests -initially a call to repeal tax hikes- have developed into a movement that has cut across Kenya's traditional ethnic divisions, becoming the biggest threat of William Ruto's two-year-old presidency.
Though Ruto withdrew the tax increases in a victory for the movement, the heavy-handed reaction to the protests has raised fears of rights backsliding, as campaign groups have documented hundreds of arrests and at least 39 deaths.
Amnesty, the Kenya National Commission on Human Rights and the Law Society of Kenya all put the number of abductions at more than 30, though they said most were later released.