Japanese officials and their American counterparts did not spend any significant amount of time discussing trade during Trump's official state visit over the weekend so you can understand why Japanese officials were surprised to hear Trump say they will sign a deal in the near future.
After Trump said the U.S. and Japan will sign something soon, Japanese officials were forced to clarify that Trump made that up.
From Reuters:
After his Monday summit with Abe, Trump had said he expected the allies to be “announcing some things, probably in August, that will be very good for both countries” on trade.
On Tuesday, however, Japanese Economy Minister Toshimitsu Motegi said the U.S. leader’s comment probably reflected his hope for quick progress in the trade talks.
“When you look at the exact wording of his comments, you can see that the president was voicing his hopes of swift progress in talks toward something that is mutually beneficial,” Motegi told reporters at a regular cabinet meeting.
We have a "president" whose statements must be clarified and explained by foreign officials.
I'm certain that everyone reading this is old enough to remember when Trump said he would sign a deal with Chinese President Xi Jinping almost two months ago if not seven months ago. And as you know, things didn't work out that way.
It's moments like this that make me think Trump will impose tariffs on foreign cars and car parts later this year because he's going to make untenable demands with the expectation that his demands will be quickly met. Trump says everything will be easier than it actually will be and what he says becomes what he thinks and what he thinks becomes policy.