The full-back opened the scoring as Pep Guardiola's side eased through to the quarter-finals with a 3-1 win but confessed that the strike was accidental.
Walker said: "It was a cross for my goal but we deserved a bit of luck with the way we were playing and I am lucky to get on the scoresheet."
City remain in the hunt for silverware on all fronts this season and Walker credits Guardiola for the team's success in recent years.
He told BT Sport: "We have made a few changes from last season tactically with pressing and how we move the ball around. The gaffer knows what he wants. He has proved it across many clubs and he has brought that to City.
"Over the last four seasons we have been very good. Last season we just got beat by a very good Liverpool team."
Walker continued: "It was a professional win and we move on to the weekend. Everyone who comes into the team does well. All I can do is make sure I am doing the right things when I am on the field.
"Every season I've been here we've always been fighting for trophies. Each and every game, we play like it is our last and try to win the game."
City have broken an English football record by recording 15 straight wins and Guardiola was full of praise for the achievement.
He said: "[15 straight wins] is a message for ourselves. We came to win which was the most important thing. We cannot deny how pleased and how proud we are to break this record from a long time ago. Records are there to be broken. It is not easy in the modern era to do 15 games in a row. We are happy for our club."