He is comfortable at either wing or first-five, and played fullback for Samoa at this year's World Rugby Under-20 Championship, alongside Kemble Frost and Darren Tiumala from Bay of Plenty.
Signing for Bay of Plenty did not go down well with the Wellington Lions management team but Tiatia says it was a simple choice.
"[McMillan] was my under-19s coach and he gave me an opportunity and was straight up about it. I loved his coaching style so thought I would come up here and follow under him. I haven't looked back yet," Tiatia said.
Tiatia is not getting too far ahead of himself, despite his match-winning role in the Steamers crucial home win.
"I guess it is always good getting on the score sheet but when your forwards are working hard, it is easier playing off the front foot. I just found myself in the right place at the right time."
Tomorrow night's clash with the Super Rugby-laden Tasman team in Nelson looks a one-sided contest on paper.
But Tiatia is having none of that.
"There are a few injuries in the team, but the spirits are high and we are looking to get down to Tasman for an ambush," he said.
"So it should be exciting. All their Super Rugby players would have had a long season so could be quite worn out, whereas we're quite new and young, so we can go down there and give it a good shot.
"Coming into the environment there was a lot of talk about previous years and how results had not really gone their way. I guess it is good we have got a taste of that winning feeling now and hopefully we can keep the ball rolling."
Steamers backs coach Rodney Gibbs says Tiatia is confident in his ability and asks really good questions.
"He has a good knowledge of the game but is a really instinctive player so we have to make sure we allow him to move around the field.
"That is where we are going to get our best gains out of him, as he has a great nose for a gap ... it is very hard to defend against players who pop up in places you don't expect."
