
No... Incoming explanation on why you completely misinterpreted the flashback scene! (I'm just copying and pasting previous comment)
Right before the flashback, there’s a really important detail people seem to be ignoring. The loaner uncle is in the car, talking with his driver. The driver asks him, “Why now? It’s been over ten years, why step in?” And that’s exactly what leads into the flashback we, as readers, see. It’s not random. It’s showing us why he’s finally choosing to act.
In the flashback, the loaner uncle had gone to collect payment from the MC’s dad. Instead, he found the MC alone in the house, trying to sleep off a high fever, with a fever patch on his forehead. That’s when he really saw the extent of the abuse. Bruises all over his body, with no one around to care for him. Just a sick child, completely neglected, while his dad was off meeting someone for fun. The loaner uncle felt guilt and sympathy, but also knew he wasn’t supposed to feel that way because of the nature of their debtor-loaner relationship. That’s why he said, “...because between us… not even a shred of sympathy was allowed to exist.”
If you reread the webtoon, you’ll notice there were hints earlier that he suspected something wasn’t right at home. But this moment is when it fully sank in. When the panel shifts from the MC’s flushed, fevered face to the uncle silently staring at him with that solemn expression, it’s clear MC's reality hit him hard.
This scene is not romantic. It’s not sexual. It’s not grooming. It’s a fucking turning point, for him as a character, and for us as the readers. It shows why the loaner is stepping in now. He wants to finally do something right. He wants to protect the MC.
And now, he wants to protect the MC from the ML and his family, because he knows the MC is going to get hurt all over again.

wait i think you misunderstood my point. i actually agree with you. my reply was for OP. To add to your point, his fascination towards yeongwoon to me leans more to possessiveness. none of this curiosity was hinted before seoin entered the scene. again, this realization hit him when seoin has occupied yeongwoons time and mind. let me be clear: ITS NOT HEALTHY! But I dont think this has any inclination to pedophilia or that sort. But only time will tell and I hope its not the case.
Ahjussi look at the child body and DEFINITELY he feel something right? Oh no no NOT IN MY HOUSE NOT ON MY WATCH i stg seo in be a better mc bro