"He's taken the decision. He's obviously not happy about the decision, but he's accepted it and said, 'Whatever's best for Queensland'."
Walters added he did not think it was fair to put Slater under pressure by putting him straight back into the team.
"It was a really tough decision that we had to make around Billy," Walters said.
"He's been a great player for Queensland, but we just felt that... Darius was Queensland's best player in last year's series and again this year on the Four Nations at the end of last year he was in the top two or three players for Australia and again this year in the Test he was outstanding.
"The second part of that is, I think it might have been just a little bit unfair on Billy to put him under so much pressure in Game 1 of the series."
Triple M Brisbane earlier reported Slater did not fly to Brisbane with Storm teammates Cooper Cronk, Cameron Smith and Will Chambers for today's Origin team announcement.
Walters on Monday admitted he was forced to make a "nightmare" decision surrounding the contest between Boyd and Slater.
"That's been the dilemma for us to try and get the balance right," Walters told Sky Sports Radio's Big Sports Breakfast.
"At the end of the day what's best for this team - that's the dilemma. I can tell you it's been nothing but nightmares for myself and the selectors about what we do there.
"It's been a tough decision that we've had to come down to. I can't tell you on the show who our fullback will be, but it was just so tough deciding who to put where and Billy - and again his form last night was good and he's a very proud and passionate Queenslander - so no doubt it's a tough one for us.
"And then Darius, his form at the Broncos and then last year for the Australian team. That's what's made it so difficult. Both of them are in such good touch."
Queensland team: Darius Boyd, Corey Oates, Will Chambers, Justin O'Neill, Dane Gagai, Anthony Milford, Cooper Cronk, Dylan Napa, Cameron Smith (capt), Nate Myles, Josh Papalii, Matt Gillett, Josh McGuire. Interchange: Michael Morgan, Sam Thaiday, Aidan Guerra, Jacob Lillyman. 18th man: Johnathan Thurston.