Being unsure would favour the statu quo. The statu quo is not what won. You have 52% who wanted to change the statu quo, and the 48% who would be divided between unsure and in favor of the EU.
Yes, to an extent. 52-48 is quite too close to mean anything other than "the Leave vote won". A lot of voters could have changed their minds either way had the vote been a week ago, tomorrow morning, or in a month.
