The Dragons were leading 34-4 in the second half but a storming final 30 minutes put the Broncos just six points behind, with the side from Perpignan hanging on for the two points.
"I was pleased with the first 50 minutes but I'm very disappointed with the last 30," Sky Sports News quotes Frayssinous as saying.
"We have spoken about the performance and not the two points tonight, it is not that we haven't won by 30 or 40 points, it is that we were not clinical with the ball. We have got a lot of work to do."
The Dragons are now fifth in the Super League.