It takes a bit of effort to learn to "read" the man. Sometimes what he says he intends you to take literally, sometimes not. Sowing confusion is part of who he is.
The fact that Trump was not being literal in this case was reported on Friday evening. The WH was asked, and went on the record, rump was referring to the WaPo article, not confirming that he was under investigation.
That the press is in high dudgeon Sunday is risible.
I knew (or thought) when I saw the tweet that Trump was ginning up the press to chase a falsehood initiated by WaPo. The remark was a sort of sarcastic irony, an absurdity of you will. What makes it absurd is taking the premise as true, that Trump is under investigation for obstruction.
Your moment of confusion and/or angst (and there are many in that boat, I'm not picking on you) is regretable but in the end minor consequence.
When lefties are confused they say and do tings that hurt themselves.