I can give you a fuller answer to that, but it's spoiler-ish, so read at your own peril:
In summary, yes. The tiny aliens came to earth in the aftermath of the events in Moon You. In the climax of PH1, they killed the super-evolved alien who wanted to Hwang Ji's immortality, and its blood, presumably containing the remaining aliens in that body, fell into the water. This seems to be causing the events in IotA now, and it seems to be the cause of the still untranslated series, Tidal Territory, which was published earlier than PH1, but depicting events that take place after both PH1 and IotA. As for PH2, we still don't know how it fits into the timeline. We also don't know exactly how TT and IotA are related temporally, but my guess is that IotA happens between PH1 and TT.