A preprint is available on arxiv [0], see the top of page 18 for what metacognitive laziness is:
"In the context of human-AI interaction, we define metacognitive laziness as learners’ dependence on AI assistance, offloading metacognitive load, and less effectively associating responsible metacognitive processes with learning tasks."
And they seem to define, implicitly, “metacognitive load” as the cognitive and metacognitive effort required for learners to regulate their learning processes effectively, particularly when engaging in tasks that demand active self-monitoring, planning, and evaluation.
The analogize metacognitive laziness to cognitive offloading, where we have our tools do the difficult congnitive tasks for us, which robs us of opportunities to develop and ultimately dependent on those tools.