We all know that men and women are shaped slightly differently. In general women are slightly shorter in the torso, hips are more angled and they have breasts.
Hence pack design needs to accommodate this. Obviously everybody is different so it is perfectly possible and I believe acceptable for a man to get a better fit with a women’s pack and visa versa. However women are far more accustomed to being squeezed into “unisex” than men wearing “women’s” designs. Hopefully one day this will change.
So what differentiates a men’s from women’s back pack?
Hipbelts should be more sculpted and angled to offer better fit around the hipbone.
Bottom line is fit on whatever you intend to buy, do your own research, if the bag does not fit properly then look at other options.