I assumed he was saying something like "the majority of women prefer a man more 'masculine' than the median man". By analogy, if it is true that "the majority of men prefer a woman who is slimmer than the median woman" it should be obvious that being overweight will make it harder for a woman to find a match even if there are men who prefer less slim women. Saying "men prefer slim women" is a slightly sloppy generalization but not an unreasonable one in this example.