Responses

To be fair he just found the woman who loved and cared for him the most (second to the old lady) dead in the warehouse in a gory way. Ahjin has admittedly been pretty sheltered so I'm not surprised he ran in fear, but whoever orchestrated all this probably expected that too. He's most likely hiding in a place only he knows, or in the bosses room
I can honestly see how he'd believe that Ahjin was the spy. Everything was orchestrated early to make him believe it. Hell, if you told me all these things Ahjin supposedly did within that timeline right after my best friend was stabbed in front of me, I don't think I'd be in the right mind to believe he wasn't responsible either.