What is your definition of 0-day? Because they are exactly right, this is a 0-day. Whether it's already actively being exploited or not has no bearing on the definition.
> normally I'd define it as something found in the wild being exploited already
Yeah, but ... that's not what it means. You can choose to define "spoon" as "fork" too, but I don't see how it's useful to go around complaining about other people using the actual definition of the word.
I'll refer you to https://en.wikipedia.org/wiki/Zero-day_(computing) to make up your own mind.