Alan Kay defined object-orientated programming as having messaging, state hiding, and late binding. I think the ship has sailed on the last one, but the first two properties hold true for at least all the object orientated languages I'm aware of.
A closure lacks messaging by default, so it's not an object. You can certainly make an object from a closure, and in an object orientated language a closure may be itself represented by an object; but responding to messages is not an inherent property of a closure.
It's not useful to say that all languages have all features; the line has to be drawn somewhere. Being able to theoretically write an object system for a language doesn't make the language object orientated.
A closure lacks messaging by default, so it's not an object. You can certainly make an object from a closure, and in an object orientated language a closure may be itself represented by an object; but responding to messages is not an inherent property of a closure.
It's not useful to say that all languages have all features; the line has to be drawn somewhere. Being able to theoretically write an object system for a language doesn't make the language object orientated.