Why would it be unrealistic for 20% of women to like women too at least somewhat? It is not stigmatized anymore. And statistically, males are more more dangerous partly due to strength and partly due to ideologies they sign up for. So, a woman a little attracted to other woman has more motivation to admit it.
The phenomenon of men having sex relationships with other men in male only environments (jail, army) existed before. They reverted to heterosexual relationships when they left the environment and would not call themselves "bi". It is opposite side of it - clearly having something out of same sex relation did not made them bi, because it would be shameful.