"The first I saw of it was on that screen, I got straight on the walky-talky and said something. There were a couple of expletives in there. Then I spoke to the players at tea time and said we would deal with it at the end of play, which happened through the process," he said.
"I am confident it is an isolated issue and a grave mistake. It's never happened before in speaking to those guys," he added.
Lehmann also backed Smith to resume his international career when he had served his 12-month suspension.
"He is going to come back a better person, there is no doubt about that. To see the hurt in him over the last three or four days, you just feel for him," he said.
Following CA's ban, both Smith and Warner were also banned by the Indian Premier League for the upcoming edition of the Twenty20 cash-rich franchise-based meet in India.
