Paia'aua, whose only appearance for the Wallabies was in 2017 against the Barbarians, was about to return to France to prepare with Toulon for the new season Australia coach Dave Rennie called him to see if he could delay his departure.
"I jumped at the chance, and I'm going to take the opportunity and hopefully go well," he told Australian media.
Having left the Reds to play in France when aged 24, Paia'aua felt he was young enough to still have a chance to return and play for Australia.
"It's just come earlier than I expected. I have been working hard overseas, and I'm glad Dave saw that," he said.
Paia'aua acknowledged the role Nonu, a 103 Test-capped All Black and two-time Rugby World Cup winner, had played in his development.
"I've grown so much as a player since I left.
"I've played with a lot of experienced players during my time at Toulon, and I've just picked up how they prepare for games and their bodies every week. My skill set has improved a lot also, so hopefully, I can get the chance to show that.
"[Nonu's] been a massive influence on me being a centre since he's been there. He's one of the best 12s [second five-eighths] to play the game, so I try to copy him.
"He's been really good to me. Every time we're on the field, he pulls me aside and helps me work on my skills, especially my kicking game," he said.
Nonu and fellow Toulon player Springbok lock Eben Etzebeth had both messaged their congratulations at his call-up.
Paia'aua has a year left on his contract with Toulon, but he admitted being in Wallabies' consideration was something more to think about in deciding his future.
"I haven't discussed anything in my future yet…Being in camp, I can see what the set-up is, so I'll see how I go and make a decision from there," he said.