This chapter was very confusing.
The whole timetable of events from the dragon napping, encountering the MC (and "friends"), the trip to the demon world, and the return. It felt like the description/order of those events kept changing and at the same time, they never actually answered the question of why the heck 10 years disappeared in the first place, where those 10 years were spent, and how in the world a normal human never noticed (or even aged?) that passage of time.
The disappearance of all the other monsters on the mountain also made no sense. The dragon made it sound like the monsters were attracted to the mountain by it's presence as it slept, but the idea that all the monsters would simply walk away without bothering anyone after the dragon left is utterly absurd. Monsters build nests, monsters need food, monsters are the natural enemy of humanity. If they said that after the dragon was "killed" that an organized sweep of the mountain was performed to clear it of monsters, then sure, that would make sense, but simply implying that a mountain full of monsters would ALL simply leave is ridiculous.
I also find it rather odd that the MC would take on the mother role for a creature much older (and exceedingly more powerful) than her. Did she somehow forget how their high level party tried to kill it, failed, and fled for their lives afterwards? Did the dragon mess with her mind during that 10 year time gap? Why does she have absolutely zero caution towards a creature that's likely listed as an extremely high tier threat? She's accepting all this WAY to easily, which makes me worry that the MC is going to be the total pushover type.