Johnson struck the winner against Stoke City on Saturday.
The Hackney-born midfielder was with Arsenal until he was 15, training next to the legendary back four of Lee Dixon, Steve Bould, Tony Adams and Nigel Winterburn.
Johnson admitted: "Basically my job is to sit deep and protect the back four. I leave it to the other guys to score the goals.
"I'm not in the box usually for set-pieces and normally just hang around on the edge of the area.
"But the gaffer's told me to get myself in there and when Snoddy found me with the free-kick all I had to do was guide it in."