"It was just confusing because there were a few other guys who got the same thing and were allowed to join in on all the training.
"I just had to ask the question why I was different."
Coach Shane Flanagan previously advocated for Barba to join Sharks training while banned, saying it would have been beneficial for his rehabilitation.
After Barba was hit with a 12-game drugs ban last November, he was released from his deal with the Sharks, only to re-sign on a one-year contract two months later.
But when the NRL delayed ratifying his deal, which would have allowed him to begin serving his time, he began to investigate other options.
Barba, the 2012 Dally M medallist, said he would look back on his NRL career with mixed emotions.
"Obviously, I would have liked it to run a bit more smoothly than my career did go," he said.
"I won two pretty special awards in the game. If I leave and don't come back, I'd be happy with how everything went. I'm ready to move on."
The premiership-winning fullback said he had played rugby union in his youth but is aware he is no guarantee to get on the field for Top 14 heavyweights Toulon.
"I've spoken to a lot of people about how good the side is over there, I might not be able to crack the side, it's star-studded," Barba said.
