Mir has now completed his £13.7million move to Sevilla, signing a six-year contract.
He was also attracting attention from Atletico Madrid but returned to training at Wolves this week after helping Spain win a silver medal at the Olympics.
Lage held crunch talks with the forward to see whether he was committed to staying with Wolves but the head coach has revealed that he wanted to return home.
He said: “It was very clear and very simple. I said to him ‘if you want to stay, I would like you to stay, but if they bring a good proposal to you and the club then it’s an opportunity for you and the club’.
“The proposal came and he accepted. I wish him all the best.
“For the time he was here it was very good for us. You can see he is a good player. The same way he wished me luck, I wish him all the best in his career.”
Mir also only had one year left of his contract and when asked if that was key to letting him go, Lage added: “Yes. It’s also important with Rafa that he was here in training three times, because one day we did a double session, and from my point of view he enjoyed working with us.
“It’s not just a question of work, but also environment and he wanted to return to his country.
“When you have a situation like that, you need to at least understand. We received a proposal and it’s better to sell him and get some money to invest in another player.”
Meanwhile, Owen Otasowie has also officially completed his £3.5million move to Club Brugge.
And Lage insists it was the right move for a young player who had his opportunities limited at Wolves.
"When you arrive in a position like him, three years in the club and everyone thinks he can be a potential player, but when it takes too long sometimes you need a different challenge," Lage added.
"For Otasowie it is the best and a different challenge for him. Maybe he can grow up faster and become the top player we want him to become.
"Sometimes after two or three years and you continue to be potential, it's better to give him a different challenge."