I thought they've been investigating him for this the whole time. It shows how long and muddled the timeline is.
Not at all the timeline is quite clear. From January to May Trump's inner circle (Flynn, Manafort, Jared, and maybe Sessions) are the subjects of the investigation, Trump wanted Comey to tell him an public he wasn't under investigation but Comey while telling him he wasn't the current subject of the investigation won't commit to "you're not under investigation" because the inner circle investigation could easily lead back to him. Then Trump fired Coney an now he is under investigation