The Iceland winger believes Defour's strike highlighted just how much quality Burnley have as they continue to challenge the Premier League's top six.
“There is a lot of quality in this team and we're showing that in each game," Gudmundsson told the Lancashire Evening Telegraph.
“We've done that and there aren't a lot of teams that come to Manchester United and go 2-0 up in the first half. I think they've only lost one game here, I think they've won every other game, so that shows how good a job we've done.
“He (Defour) takes it on one side and I take it on the other side. I was going to take it when they lined up the first wall because I thought I could bend it around it but then they fixed it. Steven said 'I'll take this one' and luckily it went in.
“It was a great free kick and to score two goals here in the first half proves we did a very good job."