Okay I could be wrong but they way I am looking at it is that they are flipping the Ecell of H20 would would mean its being oxidized. I am not sure why they didn't flip the reaction in the answers but if you were to use the reduction potential of F2 and adding 0.83 because that is what the value would be if it was oxidized, you would get the greatest voltage of +3.7V.
Rolltide has the right idea. The negative potential means it doesn't really want to be reduced and would rather be oxidized. Thus you have an ox-redox reaction. The H2O reaction has the largest negative redox potential so it is the strongest oxidizing reaction and Flourine clearly wants to get reduced based on these redox potentials. I got this question wrong too when I was studying dw about it :0