"I was with my partner at the time," Austin told the publication, before confirming it was the High School Musical alum.
"We’d been together for so long and she had this sort of clairvoyant moment and so I really, I owe her a lot for believing in me," said the actor, who is now dating Kaia Gerber.
The nomination, however, proves bittersweet for the 31-year-old following the abrupt death of Lisa Marie Presley - the daughter of Elvis and Priscilla Presley. Austin called the loss "devastating".
"There’s certain moments where it feels really strange to celebrate and a moment like this right now is one of those things that as a young actor, I always saw off in the distance as this thing that almost seemed unattainable," he said.
"And so to suddenly hear my name listed amongst these other amazing actors as recognised by the academy, it’s so surreal to me. And then I’m also filled with this really intense sorrow because I just wish Lisa Marie was here to celebrate it with us."
The actor attended Lisa's memorial, which he described as moving - admitting it was "hard to put into words".
Lisa suffered a cardiac arrest at her home in California, she was 54.
“It is with a heavy heart that I must share the devastating news that my beautiful daughter Lisa Marie has left us,” her mother, Priscilla, confirmed in a statement to PEOPLE.
“She was the most passionate strong and loving woman I have ever known. We ask for privacy as we try to deal with this profound loss. Thank you for the love and prayers. At this time there will be no further comment.”
Following the tragic news, Austin told PEOPLE that his "heart is completely shattered" for Lisa's children and mother.
"I am eternally grateful for the time I was lucky enough to be near her bright light and will forever cherish the quiet moments we shared," he said.
"Her warmth, her love, and her authenticity will always be remembered."