Everything I've ever bought from O'Connell's has been good quality and was offered at a price that was good value for that given quality compared to other full retail pricing for equivalent quality. I.e., they don't offer questionable quality, mark it up, and claim it's exceptional as do most other retailers now.
I've also found them to be very forthcoming when I've spoken with them by phone, so you might ask them who made it. Though in this instance they may be reluctant to avoid serving only as a basis for comparison shopping. And it's equally possible that the maker makes for others who charge even more and don't want O'Connell's pricing equated with their sweaters.
I.e., you'll get solid quality, won't get a bargain, but won't get gouged either.
I'm sorry, I've never bought cashmere from them, and have no idea who may have made the sweater. Though at that price, I suspect this sweater should be about as good as it gets. And if you don't like it, I'm sure you can return it.