Mancini went onto the pitch to confront referee Peter Rasmussen after a controversial end to City's frustrating and damaging 2-2 Champions League draw with Ajax at the Etihad Stadium on Tuesday.
City striker Sergio Aguero had a goal ruled out for offside in the 88th minute and Mario Balotelli was denied an injury-time penalty as Rasmussen blew the final whistle.
Mancini also clashed with the cameraman who filmed him at close proximity as he walked across the pitch but later said he had only been telling him to stop recording.
First-team coach Platt said: "Why wouldn't the manager of a football club be frustrated? Why wouldn't we all be frustrated?
"Players are frustrated, supporters are frustrated, staff are frustrated.
"Robbie has gone onto the pitch and spoken to the referee. As he comes back, he turns around and has a camera in front of his face for 30 yards.
"He turns around and says, in English, that basically it is enough now.
"People then want to start talking about what has happened and almost exaggerating the incident."
Platt added: "I don't think he is the first manager to go onto the pitch.
"If you go on to Wikipedia you'll see has done it before, not just as a manager but as a player. He wears his heart on his sleeve."
The incident came a day after Mancini had lost his temper in a press conference when asked about a previous statement that he had been "close to seven or eight teams" last season.
That in turn had come about following reports he held discussions with Monaco last season, one of a number of stories in recent weeks in which Mancini's future has been the subject of speculation.
Platt said: "We can sit here and drag it on for another three days but that's what seems to be the thing that is happening to us at this moment in time, half-voices, half-truths, stories that are probably big enough to go one day are actually lasting a lot longer than that and for what reason, I don't know.
"The manager for three or four press conferences has not spoken about the next game but about what people want to write about."
Platt was speaking as Mancini chose not to attend City's regular press conference to preview Sunday's Barclays Premier League game against Tottenham.
Asked why Mancini was not present, Platt said: "Because I've been asked to come.
"He (Mancini) has got a couple of things he needs to do. He is fine, why wouldn't he be?"