City were in control at 2-0 up before Rodri became involved in an altercation with Morgan Gibbs-White a minute after half-time.
The Spaniard put his hands around the neck of the Forest forward and was sent off, leaving City to battle for more than 40 minutes a man down.
Asked whether he was angry with Rodri, Guardiola said: "Yes. I don't like to play with 10 for our faults. I said at half-time, be careful guys. The game has been in a position where we are comfortable. Relax, control your emotions. Unfortunately Rodri didn't do it.
"Hopefully Rodri will learn. The game was perfect [for] 35 minutes and after that it became a little bit chaos. That wasn't our responsibility, that's for sure. But Rodri had to control himself and his emotions. Because I can get a yellow card but Rodri can't get a yellow card but I don't play."
Guardiola was also asked whether he expected Rodri to apologise for giving his teammates a man short for almost the entire second half.
"He has done it," the City manager said.
"Rodri is an incredible player. Kyle [Walker] has done it in the past. It's emotions, they do it. The trick is to control yourself. I cannot control myself but I don't play."
Rodri is set to be hit with a three-match ban following his red card, which would rule him out of the trip to Arsenal on Oct.8.
City have the option of appealing the decision and Guardiola said he would speak to the club about the possibility.
"I don't know, it's a question for the club." he added.
"I think Rodri has to learn. I'm not saying it wasn't a red card."