The sweater

Something I can't really wrap my head around is when Sophie1 asks Ethan2 where he got his sweater. I believe the same sweater is worn by Ethan1 when he pretends to go shopping but instead goes into the guesthouse. However, he's still wearing it after he comes back out to the car. So where did Ethan2 get the sweater?

At one point Ethan1 makes a remark about missing some clothes, and I think he hinted that Ethan2 and Sophie2 somehow took them. But this is clearly refuted when Sophie1 and Sophie2 wear the exact same clothes at the end of the movie. So why does Sophie1 ask Ethan2 where he got the sweater? Is she just testing him to see how much he really knows about Ethan1? Perhaps it was a gift from Sophie1, which means she might find it important to know if Ethan2 remembers important things like that?