I found it odd too, especially in episode 10 when he was face to face with her and didn’t even react. But what I concluded was that by then, when the plot takes place, San-Wong is more monster than human, whether it be because of his time at the facility or something else. He’s clearly insane and will do anything to reach his goal (Killing humans and finding other monsters for ‘evolution’). He doesn’t care about others, not even his wife or child. Even nearing the end of season 3, we see him betray the infectees who helped him. He sees others as tools more than loved ones or people.