In the light novel the reason he stayed behind was because he'd just cured his mother and wanted to spend time with her and his sister. The president of the association was curious why he'd refused and then found out the reason why.
All the Japanese outside got wiped first - the cameras and 'shadows' hadn't been placed on them, so Jinwoo didn't know. Then shit hit the fan all at once inside the cave and he immediately teleported over.
@NOUN that's such a bad analogy, should he place a shadow in each country at all times just in case someone sometime might appear and be a potential threat? does he have an obligation to participate in each raid above A? there were several S class there and the guild deemed possible to clean the raid with just that, at that point THERE WAS NO REASON for him to participate, absolute 0. Yet, he was cautious to place a shadow just in case something goes wrong, and now that something went wrong ... NOW HE HAS A REASON. Or else he might as well get ride of the whole guild system if he has to do everything... Remember, his main reason to fight was to cure his mother and he did that already, let him enjoy that.
I know there is a competition between JB and SL to put out the release the fastest, but some QC would be nice:
I.E.
SL: Ryuse Kang
JB: Liu Zhigang (official translation)
SL: 'We have lost our Queen. The life of your lowly conscript… doesn't balance the equation...'
JB: 'The Queen was attacked here… Even if you guys killed the guards… it doesn't make sense...'
(clearly one of the groups was making stuff up here)
@HikariGo A translation from the LN online goes
"This side... Queen, dead..... Killing Soldiers..... Not enough payment... your king, who?"
So it would seem both sides are screwing up in about equal measure, at different parts.