I imagine you might have been a little shocked if this is something that isn't normally done in your office; but, my hours were cut down to 32 in April along with six other people. We were given the choice of taking a whole day and what day we wanted to take, or shorter work days. Once everyone's schedule was set an office wide email was sent out to let everyone know.
I guess in our case it was a little different in that it would be very noticeable every Friday that 5 people were never showing up (one person took shorter days and the other took a Monday).
So, to me I don't really think of it as private information.