Dortmund more than likely bought him now to give the opprtunity to sell him in the summer for twice the amount or morw.
Will he have another season like this next season?
Do many here think that Paco was some unearthed super player that we hindered, or that he is a very good solid striker who with confidence, form and a setup suited to his strengths (with gametime and less pressure) is playing at an incredibly high level right now. Think Rodrigo last year compared to current form, Vardy in the Leicester title winning season or Iago Aspas returning to Spain from Liverpool.
Great business to sell him now. There is a flip side to this coin too. If Paco gets injured or just loses form in the second half of the season, Dortmund may very well have opted not to buy him.