"If Strider had walked away, my dad would be alive," Jason Rowley told the judge at Diem's sentencing hearing.
Diem, 34, was charged with murder, or manslaughter in the alternative, and misdemeanor counts of assault and criminal mischief.
In January, Diem pleaded guilty to lesser third-degree felony counts of homicide by assault and aggravated abuse of a vulnerable adult.
Johnson sentenced Diem to prison for a zero-to-five years on each charge, and ordered them to run concurrently.
"This was a tragic event that didn't have to happen," Johnson told Diem. "A good man's life was cut short and that is nothing short of a tragedy."
Diem had apologized for his role in the fight.
"I have major responsibility in this," Diem told the judge. "I'd like to take responsibility for my part in it and move on ... I feel bad for my mom, her loss. She lost her husband. I can't imagine what that would feel like."
Defense attorney James Wright had asked that Diem be sentenced to two years in the county jail, with credit for time served. Wright said that while Diem hit Rowley "pretty good" four to six times that June night, emergency room doctors said the stepfather had actually died from a massive heart attack.
"One of the doctors said to me, it was a ticking time bomb," Wright said of Rowley's heart. "Unfortunately for Strider, it went off after he punched him ... It could have happened at any time."
But Deputy Utah County Attorney Tim Taylor said the official cause of Rowley's death was "blunt force trauma to the head, which caused cardiac arrest." He asked the judge to send Diem to prison.
"This was a wild man out of control," Taylor said. "... I think prison is the appropriate punishment for the man that did this."
Orem police say that on the evening of June 26, Diem came home to 1615 S. 400 West, where he lived with his mother and stepfather. Diem's mother suspected he had been drinking and pulled a bottle of whiskey from his backpack, according to police.
The mother poured the whiskey down the bathroom sink, which agitated Diem.
"He started to argue with her; at one point, she says he 'poked' her in the nose," Orem police Capt. Ned Jackson said at the time.
Diem's mother and stepfather then forced him into his bedroom and shut the door. But Diem broke out, and the trio continued arguing until Diem's mother struck him in the head with the whiskey bottle, which shattered, according to police.
Diem then attacked Rowley, hitting him several times in the face and knocking him to the ground before leaving the house.
After the altercation, Rowley told his wife he was fine, so she followed Diem outside and told a concerned neighbor to call 911.
But when Rowley's wife returned, she found him unconscious and not breathing. The man was later flown to Utah Valley Medical Center, where he died at about 1:30 a.m.