Leon Best had put the hosts into an 18th-minute lead with a header after they started brightly.
But City hit back within three minutes of the break and it was a screamer from record signing Maynard.
Johnson said: "He's scoring goals like that all the time in training. No goalkeeper in the world was going to save that.
"It came from a good move from us and I wanted to see more of those types of moves but he's hit from 25 yards and it hit the underside of the bar before it went in.
"He's got some good ones this season but that might just be his best one."
He added: "I thought a draw was a fair result. I wasn't happy at half-time because I hadn't seen our pattern - there was too much kick and rush - but I thought it was better in the second."
Coventry had the better of the first half and were left to rue the fact that they did not have more than one goal to show for it.
They took the lead when Marcus Hall crossed from the left and Best headed low down past Dean Gerken in the City goal.
Michael McIndoe's long-range free-kick almost handed him a goal against his former club but it was deflected onto the post and behind.
From the resulting corner, Best volleyed over the bar before Clinton Morrison had a second goal for Coventry ruled out for offside.
At the other end, Coventry goalkeeper Keiren Westwood made a fine save to deny Alvaro Saborio on his debut but the Costa Rican played a big part in the equaliser at the start of the second half.
He knocked down for Maynard to hit home but Sky Blues manager Chris Coleman felt he had handled.
"Take nothing away from the strike," he said. "But we felt the referee should have blown up for handball twice in the build-up.
"We were disappointed to have that second goal ruled out for offside because if we had gone in at half time 2-0 up, we probably would have gone on to win the game.
"But this has stopped a little run because we had lost two games in a row. We have got a point but we feel we might have had three."