Johnson felt Dan Burn's second-half header crossed the line but referee Andrew Madley adjudged it did not.
The Londoner said: "I think there was a header where their goalkeeper saved it off the line. We will have to look at the video because we genuinely felt it was over.
"We knew they are an experienced side and have players who show a lot of passion, and we had to match that.
"It was a great game for a 0-0, and made for a good atmosphere. It felt like a Championship match.
"Like when Manchester United play Manchester City, it could have gone either way. They created some chances, as did we.
"I think their goalkeeper was probably man of the match for me. I was pleased with our performance and if we can continue to perform like that then we continue to get results.
"I felt our performance was good enough to win that game - and that was what I was most pleased at."