It is absolutely a lubricant - it is a combination "lubricant, rust preventive, penetrant and moisture displacer". Whether it's the correct or best lubricant for many applications is iffy, but that doesn't mean it isn't a lubricant!
From personal experience, I can count on one hand the number of times that wd40 (edit: at least the canonical formulation) has been the best lubricant for a given application.
Is it? Please explain and provide sources. Just because it feels like a lubricant and maybe advertised as a lubricant it might not actually be a lubricant.
Point being, if you're using it as a lubricant, you're using the wrong stuff. What it leaves behind isn't very useful as a lubricant... unlike, you know, an actual lubricant.
My recent trip to the ground was sufficient proof to me that even water is a lubricant.