Carney scored two tries and was sin-binned in the Red Devils’ 32-16 victory over the Tigers.
“Justin has been great this week and we spent a lot of time speaking about situations exactly like what happened,” Watson told PA Sport.
“He’s a big player for us. I spoke to him all week about him playing here and he was adamant that he wanted to play.
“It’s an experience this game for him. It’s probably something he’s never faced in his life before, obviously on the back of his actions.
“To be fair to him, all week he’s been really good and said the right things, but the emotion kind of got to him. Jake Webster has slapped him across the face first on and then he’s lashed out again.
“He’s a guy who’s made a mistake but he’s a genuinely good guy.”
Salford managed to hold off Castleford in a physical encounter at the Jungle.
“We haven’t seen the game out over the last few weeks so it’s pleasing to see it out,” Watson said.
“You know you’re in for a tough game coming to Castleford so to come here and get the two points is a massive result for us.
“Cas are a good team and they’re what we spoke about as a group at the beginning of the season – you build a squad with no idiots in the group and who all work hard for each other.”