Beginners, by definition, are guessing 100%. Some will guess high, others low, and the rest in between. But they are all guessing. Perhaps There's a cultural bias to over-estimate their skill? Perhaps there's a nudge in the process of the study that led them to overestimate?

The lede isn't that people over-estimate their skill level. The lede is, why would that be as they have nothing else to go on. That is the trigger or triggers? And to say, the more experienced estimate better? Well, duh.