It looked as if the Bluebirds were going to remain seven points behind the top six after Joe Ralls struck to make it 2-1 in the 70th minute.
But Adam Armstrong completed his brace in the 90th minute to steal a share of the points for the visitors.
McCarthy said: "I've not mentioned the play-offs on purpose since I've been here. We're nine points adrift, with five games to go, so it would require an unlikely set of events.
"I know we had a great start when I came in. Everything was going well, but I was never fooled to think we were one of the best teams in the league. We were just having one of the best runs in the league.
"The players were very disappointed at the lateness of both goals, but certainly the equaliser in the second half. We should be able to hang on to that. Everyone is feeling the same way, they're all sick about it.
"I don't know the other results, but I thought even before today, eight points adrift with six games to go, was an unlikely sequence of events.
"Whether we won all our games or not, the other teams are capable of winning theirs. All we can do is look after our games and performances and results."
Will Vaulks had given Cardiff a first-half lead with a powerfully struck free-kick before Armstrong capitalised on a goalkeeping error to score his first of the afternoon and end a six-match goal drought.
The draw was Blackburn's seventh game without a win, but manager Tony Mowbray was pleased to see Armstrong rediscover his scoring touch after a spell out with injury.
"Adam Armstong is a goalscorer and that's the bottom line, you give him an inch, he'll score a goal," he said.
"He should have scored in the first minute, but he's a bit rusty. It's not like you can push a button to get him back to where he was.
"He may have scored three or four on another day if he was up to speed. But he's helping the team compete in every way he can.
"We're disappointed, as a team we know we have to win these games, in this recent run that's been the case with half of these games really.
"We've dominated most of the games we've had but Adam Armstrong hasn't been able to score, but today Adam got back to what we know he can do.
"We had 20 shots, we still need to score more goals and win these games.
"We didn't lose, we showed spirit and character, we always try and find the positives and we didn't accept defeat."