Yes. However, as it was reported at the time, it was basically sold for a reported 18 million, with two clauses saying "if they stay up, then we have an option to buy him back for a bigger sum than he was sold for" and also "if they go down, we have an obligation to buy him back for a figure less than we sold him for".
What we don't know is what the actual figures are, or what further clauses and so on there might be that will not be actioned because they're going down, not staying up - for example it's common for "if he gets capped for England" or "if he scores 20 goals in a season" or whatever. Add ons, basically.
Anyway, it seems certain he's coming back here at the end of the season. What happens after then, who knows. Unai clearly wanted to keep him under our control, though, so maybe he'll be part of next season's squad.