Nuno claimed Mason 'does not have the quality to whistle a game in the Premier League' after Monday night's 2-1 defeat at Burnley.
The Portuguese has since been contacted by the FA to explain his outburst ahead of a potential charge.
And when asked about the situation and whether he stands by everything that he said at Turf Moor, Nuno said: "We have received a communication. We will submit our thoughts on the 29th, but I can speak about it now.
"I should apologise, first of all, for the timing of my comments. They probably were not in the best moment.
"I will apologise on my timing, but I will not apologise on my words and my thoughts.
"I never, ever will judge or question the integrity of a referee. I never did it, and I will never do it, in my life.
"But what I said is about the ability of the referee, what I felt and what I saw – on the match and previous matches.
"We are in the best competition in the world, no doubt about it. The Premier League is the best competition – the only thing missing is the fans and we hope they return soon.
"We expect high levels of performance, high standards. As managers and players, we always want to improve.
"And what we expect from the referees is to be confident and maintain their authority on the pitch, to control and handle the players, and to handle the game.
"This is what we want. We want referees to improve because us as managers, we have to improve.
"Every time Wolves doesn't perform, I'm the first one to admit it, and we didn't perform so well.
"Our thoughts are always the same – we want to improve – and we want the best competition. The best players, the best managers and the best referees."
Once Nuno submits his observations next Tuesday, the FA will then have three working days to decide whether or not to sanction him.
"We expect what we expect from the referees in general. I think the Premier League has the best system of referees," said Nuno.
"When we go to a match, what we expect is the referee to not be a protagonist of the situation.
"We want the referees to let the game flow, and especially to control the players.
"Refereeing a game can be a tool to teach – to make players understand it's a tough job, as long as the referees maintain the dialogue."
On if referees should perhaps come out and explain their decisions after matches, Nuno said: "I don't see the point as maybe that would raise more issues.
"I think everyone is entitled to their opinion. But I think the Premier League has the best system of referees."
Nuno, who has been reluctant to focus on referees in the past, added: "I never did it, and I will probably not do it again.
"But I would not be comfortable if I didn't say it, this particular situation, because we want to go to a match not worrying about who's the referee of that game.
"Every time, unfortunately, we had problems, so we just don't want them to repeat."