It could be a case of the diluted TO creating less static when wiped on, and so attracting less dust to it. At some point, the mineral spirits will evaporate to the extent that the remaining TO is as sticky as it would be undiluted, so to my way of thinking, it should collect just as much dust if it was due to stickiness alone.

You could always test this idea by taking a bit of scrap wood, applying diluted and undiluted TO to different areas and then compare the dust that sticks to each one after it's dried.