In my neighborhood for a while someone (probably a group of people) were sticking vulva drawings everywhere. Building walls, lamp post, mail box, etc. They were all unique and hand drawn too.
Much like the term balls, which are only on the inside, has come to be colloquially used as a synecdoche for "testicles and scrotum", vagina gets used the same way to encompass "vagina and vulva". Besides, the clinical definition of vulva includes the vaginal opening, so it's not exactly a huge leap to the colloquialism.
I was going to “ackshually” and post a (disclaimered) medical image poking fun at the word “hole” but, as it turns, porn has completely superseded medical images of the vagina on most search engines. An internal view of penetrative sex isn’t my kink but it’s apparently a common one.