To write a play

I mentioned in this post that Coelho Netto is a Brazilian playwright whose work I have been observing.
Anyway Netto wrote this one play called "Os misterios do sexo".
The translation of the title is "the mysteries of sex" and sex in this case refers to gender, not to the act of having sex.
The play is about a teenage boy whose genitalia was not obvious at birth. His mother then decided that he was a girl and raised him in such a way but as he reached puberty he started acting like a heterosexual teenage boy which unleaches all kinds of reactions in his family ( the play was written in the early 1900´s).
In a nutshell that´s it.
What has intrigued me is that Coelho Netto got the ideia from an article that ran in a Rio de Janeiro newspaper at the time.
Books on acting always tell you to know the reason a playwright wrote something and try to figure out the character from there. Is this really plausible?
I read this piece today. If a script followed such a method would it be reasonable to expect an actor, who happens to play one of the characters, to know what is intend? I think not.