The Olympic teammates posted pictures of themselves brandishing high-powered weapons in a US gun shop on social networking websites.
As punishment, the Australian Olympic Committee (AOC) has ordered the pair return home from the London Games as soon as their events conclude.
But fellow teammate Eamon Sullivan said they boys hadn't done anything wrong.
He has questioned what the fuss is all about because in 2007 Swimming Australia took the team to a Canberra rifle range as part of a bonding session.
In a statement, AOC spokesman Mike Tancred said the two matters were unrelated, and Monk and D'Arcy had been sanctioned for "breaching their team agreement as members of the 2012 Australian Olympic Team".
"The Canberra gun range visit was an initiative of Swimming Australia," he said.
"It had nothing to do with the AOC. It was 2007, they were not members of any Olympic Team at that time.
"It has absolutely no bearing on the decision taken by the AOC at the weekend."
D'Arcy and Monk returned to Australia on Friday and quickly apologised for the photos, which appeared on Facebook and Twitter before being pulled down by Swimming Australia.
The 24-year olds will meet with Swimming Australia officials this week.
D'Arcy is a medal hope in the 200m butterfly in London, while Monk is in the 4x200m freestyle relay team.