"He went up by himself. If a player looks over to the bench all the time there is a problem. It was just an instinct," said Coppell.
"I've seen him score for us before in a pre-season game two seasons ago at Bromley. We got an injury so he played out-field.
"He does that regularly in training. All goalkeepers are frustrated centre forwards but he is a good player and a natural athlete.
"If you look at the goal, as the ball is delivered and Duberry has a great header which a defender saves on the line with his chest, during that header Federici is on the floor and the next minute he is up on his feet to finish it.
"It was like goalkeeping practice where they make one save and have to get up to make a second. I'm sure that helped him."
City boss Dave Jones was far from happy with the time added by referee Andy Hall.
"I've got to get one of those watches that referees have because you stay younger longer," he said.
"What's the point of putting four minutes up and playing one-and-a-half-minutes over?
"We should have defended the corner and it is disappointing we have not come away with another two points.
"The reaction of their fans being happy to get a point shows how well we played. The referee, for both teams, has got a lot of things wrong.
"If it had gone out for a goal kick, as soon as we'd kicked it he would have blown. But because it was a corner he didn't and you would have to ask him why.
"There was nothing for it to go on for a minute-and-a-half.
"We have had him before and we know what he's like.
"He sits next to our dressing room and he can hear everything that goes on so if I give him a piece of my mind from behind a wall I can't be blamed for that surely?"
Coppell, not surprisingly, disagreed with Jones' assessment.
He added: "The extra time was created by them as there were so many cumulative fouls.
"The cumulative breaks created the four minutes. I can't see any complaint there. Referees aren't trying to do us a favour, they are there to be arbiter."
Coppell did wonder why Chopra stayed on the pitch. Chops was booked for fouling Federici but later appeared to obstruct the Reading keeper, my own view, watching from 20 yards away was that Chopra was just jogging by, Federici didn't know he was there and any obstruction was accidental. Chopra could have run past the keeper a bit wider but he did no wrong.
"Chopra had every right to go for the ball with our goalkeeper, but he was booked for the challenge," said Reading manager Coppell. "Then he stopped our keeper kicking out and, if it had been any other player, that would have been a booking.
"But the referee gave nothing. Why?
"We were grateful for a point when Adam Federici scored, but overall I felt we deserved it."