Nothing wrong with asking don't worry.
Personally I interpreted it thet he let them go when he saw how happy they were that they could escape the miserable life they had back in Korea. And he was on vacation in Hong-Kong anyway so probably he can't arrest them while not in his territory. If there will be a side story it will probably show that he reported their seething there but they went somewhere else in the meantime because mc saw that he saw them too

Guys idk if this may seem a stupid question but why did the officer let them go?? Im not rlly good w ts pls dont attack me lolzz(maybe im js sleep deprived for not understanding this)