Sinfield, the first rugby league player to be nominated for the prestigious individual award, received 278,353 votes, 28 per cent of the total cast.
An outsider when the 12-strong shortlist was announced earlier this month, Sinfield emerged as runner-up to Davis Cup-winning tennis star Andy Murray, who collected the award for the second time in three years with 361,446 votes.
Yorkshire athlete Jessica Ennis-Hill, who had been second-favourite behind Murray, was third on 78,898.
Hetherington attended the event in Belfast and believes the massive backing for Sinfield will change perceptions of rugby league as a northern-based, minority sport.
“The BBC people were saying how influential this will be for the game,” Hetherington said.
“They were staggered, they had absolutely no idea Kevin would get the level of support he did.
“It has sent reverberations through the BBC. For Kevin Sinfield to be the second most popular sports personality in the country is quite significant.”
It was only the fifth time the code has been honoured at the BBC’s annual review and Hetherington added: “Even if Kevin hadn’t been in the top three, the week leading up to the event was terrific for his profile and that of the Rhinos and rugby league.
“We have waited 61 years to have someone represent rugby league in Sports Personality.
“We could not have had a better ambassador than Kevin and it provided an opportunity for the whole sport to work together.
“To get 280,000 votes is way above what anyone expected when the nominations were announced and is a remarkable effort.
“It was a great end to the year for both Leeds Rhinos and the game and a great platform for next year.”
Hetherington admitted he was “surprised” by the amount of interest shown in Rhinos by other guests at the gala event at the SSE Arena.
“In rugby league we all feel nobody thinks about us and nobody cares about us, but you go to an event like that and the opposite is the case,” he stated.
“There was real respect and warmth for our sport, our club and team.
“We were genuinely surprised how much they knew about us.”
Sinfield switched codes in October after captaining Leeds to a clean-sweep of domestic trophies. He will return to the field on Sunday, when Yorkshire Carnegie face Rotherham Titans in a Championship derby at Headingley.
“I will be back in training (today) and that’s the way I like it,” he said.
“The last three weeks have been manic, but the whole experience has been so humbling and I am so grateful to the rugby league family.
“It has been a wonderful experience and I have been proud to represent the Rhinos and rugby league.
“I was just happy to be in the 12 nominees, to show people what rugby league is all about.”