It's probably because the glass is rejecting the vodka.
After all, there is no such thing as a Martini made with vodka.
A Martini is a drink made of gin, vermouth & an olive.
A drink made of gin, vermouth & an onion is a Gibson.
If just changing the garnish changes the drink's name,
one clearly cannot change the primary ingredient & keep the name.
You, sir, were drinking a Kangaroo. If you added vermouth, that is.
Just a little anal-retentive Public Service Announcement
from a snotty purist.
