Agreed it is odd but never just assume siblings are an in.

This is weird. Wouldn’t the admissions director typically call in this scenario?

I think you need to ask admissions for feedback. It could be their way of saying they they had no spots or it could be there way of saying that the school isn’t a fit for your child.

We were a sibling applicant this year and wasn't the first year DS was eligible to apply. Not that unusual to wait for other DCs I think. Worked out for us but was an expansion year and even still we knew there were no guarantees.