I agree with the tapir/baku. I don't know that Matías would come up with it on his own, nor do I think the act of eating dreams in itself is enough, but I think Robert giving him the suggestion and teaming up to help Asterion from multiple fronts would be a good way to handle it.
Having someone that could communicate with the narrator would also be helpful, be it the MC or someone who is acting as a conduit. Basically a team effort to show Asterion how many people care while also being realistic about how many more lifetime worths of experience he has than anyone else in the hotel.