The incident came after a member of Charlton's coaching staff had previously kicked a ball back on to the pitch with the score at 1-1 after the game had already restarted.
But McCarthy insists it was all handbags, telling the club's official website: "We're top of the league and desperate to get points to get promoted and they're bottom of the league and desperate to get points to stay up. There's bound to be a bit of blood pressure flying around. That's all it amounted to.
"The two Charlton lads weren't happy I'd dropped the ball behind me but when I asked if they'd have done the same they said 'yes'. I said 'well shut up then' and we were laughing but Phil wasn't happy.
"That was the sum total of the 'spat' between me and Phil if you want to call it that."