Standing down: How Trump decided that not striking back was his best option on Iran

Playing chess, they made a move but it did not affect the board, so why make a rash move, let them be the aggressors. But be willing to hit hard if they do attack a second time.

One could read into this quite a bit.
Supposedly, the Iranian missiles are accurate enough to put them in the area of barracks instead of where they landed. Did they miss on purpose? Hard to say. For all their "accuracy", I can't help but note that four of the 15 missiles failed in flight. That hardly demonstrates reliability to me.
The Iranian media reported that 18 US servicemembers were killed in the strike. With no way of actually knowing that (and it being patently false) that implies strongly that it was a pre-planned report designed for domestic consumption. AKA "We showed those Americans how tough we are".
That the Iranians told the Iraqis what they were doing (not surprising) and the Iraqis told us (a bit surprising) shows that despite the recent Parliament vote, not everyone in Iraq has turned on us. That is noteworthy.
If the Iranians would have killed any US service members or caused significant damage, we'd have probably retaliated. Let's just be grateful that is not what happened.

Now the Trump administration is steadily strangling Iran's economy. That grip on their throat will get tighter now. I think we will see a pause in overt activity for now, but the covert stuff will likely ramp up.

I have to say that only Army troops could move the bases while the missiles were in flight and ensure the missiles missed their targets. You would never see the Marines or Navy move that fast. :)