Well when I read smart casual I think like a shirt and jeans maybe, I personally went for the shirt and tie option and as far as I could see there was only me and one other of the 20 people there that opted for that. there were a few that that ahd gone for the shirt and jeans but there were a few who where in a t-shirt, jacket and jeans or similar (I'm sure I see one guy come in wearing a lacoste tracktop)
I suppose as stage 1 is more informal than the other stages as it is more a way to cut down on numbers etc. it does not particuarly matter but I would have imagined people showing up trying to impress with a smarter look.