The crowd's attention was fixed on McCaw and they made sure they got as close as they could to the rugby great, who is in Buenos Aires as an Air New Zealand brand ambassador for the airline's inaugural flight to the city.
"I think one of those special things about rugby is you travel all over the world but everyone who plays the game plays as a team," McCaw told those gathered.
McCaw, who retired from professional rugby last month, said he wouldn't miss the training, but thought he would miss the sport when the team played next year.
"Unfortunately you can't play forever, I've had a pretty good run."
When asked who the best All Black was, he diplomatically answered: "There's a lot of good players I guess. A guy who I've been lucky to play with is Dan Carter. In the [Rugby World Cup] final his kicking was sensational and he's been great for a long time."
Former teammates Julian Savea, Ma'a Nonu, and Ben Smith also got name-checked by their recently retired captain.
McCaw also paid tribute to the late Jonah Lomu, who died last month.
"He is one of our absolute superstars of rugby. You go to anywhere where rugby's not really known and one [name] they do know is Jonah. So it's really sad he's passed away at age 40. He's a legend of the All Blacks and a legend of rugby so you feel for his two young kids and wife who have been left behind," he said.
McCaw also brought up his 2001 debut for the All Blacks during the question and answer session. "Because you grow up having a dream of being an All Black and once you get on the field once no one can take [it] away from you," he said.
He said the game against the Pumas at the World Cup, when he was sin-binned, was the tightest they had and that they were lucky to sneak away with it.
His advice to the young fans watching was to work hard and put in all their effort when playing.
Asked who his best friend in New Zealand was, he said: "In the All Blacks it depends what you're doing, if you're looking for a night out you stay away from Tony Woodcock, or you go see Tony Woodcock, but he's been in the same team as me since I was 18. I've have to a lot to do with Dan Carter over the years ... I've got a pretty good friendship with him."
About 40 primary school-aged boys ran rugby drills before McCaw arrived at the event, which former Pumas captain Agustin Pichot also attended.