Jay Bothroyd saw his long-range strike come back off the underside of the bar and referee Andy D'Urso pointed to the centre circle after the linesman signalled for the goal.
But McDermott said: "He guessed. He could not be sure the ball was over the line. It was not a goal. It was as simple as that.
"The linesman killed the referee and he will be embarrassed when he sees it again.
"I knew straight away that it wasn't over the line and it took me just three seconds after the game to view it again and confirm it wasn't over. It was a really poor call.
"It's 2010 and we still don't have goal-line technology. It is becoming farcical.
"But the last thing you want to hear is another manager moaning.
"I didn't think we would be talking about a draw when we were ahead but all will be forgotten in a week's time."
Cardiff manager David Jones had a different point of view, saying: "I know Brian is going to be a bit upset but on the video we have seen it looks over.
"The linesman has to make a decision but I can be upset in the first half that a goal wasn't given for us at one point.
"The ball does look over from what we have but if I was in Brian's shoes I would do the same.
"But Brian wears glasses and if he can see from where he was then I want some of those as well."
Jones was pleased with a point even though his side missed the chance to leapfrog QPR at the top of the npower Championship.
Noel Hunt had put the Royals ahead in the fifth minute when he prodded in Simon Church's cross.
"We only had 18 players for this game and just six on the bench," added Jones.
"For the first 45 minutes we didn't get the pace of the game but in the second half we did better.
"It was a pretty open game and I thought a draw was a fair result.
"You are not going to come here and see the other side not create chances.
"I am disappointed we haven't regained the lead in the Championship but every game in this league is tough.
"After the loss against Swansea on Sunday everybody was down but we showed character.
"It was two good sides having a right go at each other."