Basically, the question is whether cooling would occur if molecules of every speed in a liquid had an equal chance of escape from the surface. The answer given in the column is no, with a rationale that the cooling occurs because the faster ones are the ones that are leaving and the slower ones are left behind.
The reason I ask is because I used to use somewhat similar logic but stopped, and now I'm not so sure.
I stopped for two reasons. First, the "slow molecules left behind" implies that the remaining liquid becomes cooler than the vapor that is produced. Second, I feel it obscures the fact that the process of leaving (which is a sort of bond breaking) requires an extraction of energy from the surroundings, regardless of whether the molecules involved were initially going faster or slower.