In this case, the absolution is valid as long as the priest gives the absolution with the correct formula and performs what the Church requires, because he is expressing, 'I absolve you.' We may not know his deeper intention, which is something we cannot control, but we can assume that he wants to absolve. Otherwise, it would be a fake show. In rare cases, when a priest does not want to absolve but still says the absolution formula, I think the sin is forgiven. Even if the priest says, 'I consider this not a sin,' and then correctly applies the formula of absolution, the sin is forgiven. Of course, the sin is already forgiven when you repent of it and go to confession with perfect contrition. Once you have perfect contrition, the sin is already forgiven by God. Therefore, from this point of view, the sin is forgiven.