Given that this is an AU with people that had an animal characteristics, it must have meant that he was a mutant from that animal that children likes snuggling with.
Also there are just these people aside from family that children are comfortable being with, and at natsuki's age that time, they like hugs a lot, especially when they're close to heart, which is the chest area. Why would that be? Because their mom's heart beat calms them, a kind person with motherly feel also calms them.
One thing becomes evil and bad if you add or twist a narrative and see it that way. Now if natsuki in his preteen/teen age years and an adult sought relationship with him, that's a different story.
And true, there are plenty of stuff that are really bad yaoi out there, but please just read fluffy shounen ai if you want to enjoy BL or other stories and don't dig deeper for your peace of mind. Ban yourself from ones with animal characteristics, or ABO universe. Don't seek out ones with smut, mature, and adult tags. Definitely not BL webtoons cuz they're too liberated with their themes. And most definitely not with psychological tags because if this story ticks you off, I don't know what you'd feel about those. It's a tag not for those with perspectives that follows a straight line.
Is it that bad (aka pedo)? Not really. Until an adult makes a move to a minor, it's not. Was the adult even subtly seducing or hinting of making a move on a minor? Not really. If a minor grew up and made a move to their elder - that's on them because the elder did not make a move the whole time. Stop pillorying attractive people for being older.
I have worked in crisis center in my previous work life and I have seen true pedos.
Besides, there are really really bad yaoi here that should be pilloried. Leave this one alone.