Bishop likely wins this in the end, the absentee breakout advantage for the GOP is less than the registration advantage for the district. Taking into consideration the likely higher turnout on Election Day itself the gap between Election Day turnout and absentees is likely even larger. Also heaviest concentration of the absentees is of course the Hamptons, which is a strong area for Bishop.
I haven't seen anything but confusion on the part of the NY political blogs, what makes you so sure, out of interest? Is there an article somewhere that explains? Seems like this could be the closest race in the country, hard to see which way it'll fall.