I don't think I've ever seen a single chromebook in the wild being used by a real person for real. I am sure they exist of course. I must have even seen one and forgotten it. But in all the years since they have existed, and all the varied people I've come in contact with in all those years, if I can't think of any, then the percentage is low.

I think a relative's kid had one issued in high school a few years ago. There you go. One out of who knows how many hundreds, and that one was not even a voluntary purchase. In fact that same kid built himself a budget desktop gaming & streaming rig when deciding what to do with his own money. So I wouldn't even call him a chromebook user. The chromebook was just school equipment he had to operate like a copier or projector.

I haven't done any investigation but some scraper and/or bot configuration uses OS X as its user agent.

I run an unpublished service used by 1s of people and was hit by an influx of supposed OS X user agents that didn't correspond to my actual user base.