@Shamz Rape is rape because one party takes it from the other by force, without allowing objection or basic autonomy. The fact that the rapist's "force" in this case consists of drugging the MC without his knowledge instead of straight physical violence & coercion doesn't change the morality or purpose of the rapist in this case. See: date-rape drugs.
Now, if the two of them had gone home, got mutually drunk, had consensual drunk sex, and then she woke up first and left - that would still be an asshole thing to do, but it wouldn't be rape. But that's not what happened here.
@Kayriel I prefer the Charles James Napier approach:
[In response to Hindu priests complaining to him about the prohibition of Sati religious funeral practice of burning widows alive on her husband’s funeral pyre]
“Be it so. This burning of widows is your custom; prepare the funeral pile. But my nation has also a custom. When men burn women alive we hang them, and confiscate all their property. My carpenters shall therefore erect gibbets on which to hang all concerned when the widow is consumed. Let us all act according to national customs.”
Different crimes, same problem.