Reported as loan, i believe. But there's some interest in Spain for a permanent as well. Multiple clubs, most notably Real Sociedad wanted him, but Villareal insisted on a loan deal (probably with some kind of first refusal clause to buy) as part of the Gabriel deal.
Either way, i believe Joel will do really well in La Liga. Probably going to be the next Carlos Vela. I feel he will thrive in the environment over there, our disciplined passing ways never suited him. Always looked so uncomfortable whenever he had to play a combination play for us.
Oh, and everyone will moan at Wenger for letting him go once he puts in a few good performances. Most definitely.