Reasons why the plot twits makes totaly sense

1- Everytime SHA had a flashback to that day, there would be something different.
2- All the lies he made, even when they weren´t necesary.
3- Sometimes he was sus, and too much observant of the situation, as if he knew something they didn´t.
4- When he said he will kill the person DJ likes, that was a littler out of place too.

Until ep 13 I thought he has just bad memory or was just fooling around, but now if you connect all that, they fulled us but there where hints for sure.

 PhantomLady:

I found it suspicious  too that there were 2 different merories

1. One were he arrives after the accident and sees the boy on the ground

2. And one were he tries to stop the van from rolling down the street further. 

But know everything makes sense.

Exactly. And people say there were not clues, They just didn´t put it in a way we would necesarily doubt the character.

Just finished it and agree. At first I was wondering if he suffered from some kind of post traumatic stress disorder caused by seeing this terrible accident and that's why his memories altered. 

At the same time I also thought, maybe the accident didn't happen like we believe it did at this point. 

With every clue we got, it came to my mind that he's not what he looks like. He acted very strangely when he found the photo too. Something felt really odd and it wasn't just that he seemed to have abandoned the boy and not call for help. Even the moment when he just goes back to work after getting the gifted jacket by Tae Hee even though he wanted to tell him something. It all clicked into place in the end.