The ECB, SNB and BOC have all come out and said they didn't intervene in the yen. The Japanese MOF also said they didn't do it alone.

The Treasury here is 'acknowledging' Japan forex intervention which sort-of implies it was just Japan but unlike those other central banks they're not distancing themselves from it.

Note that the last two major US bull markets both didn't end on their own, it took coordinated intervention.

Update: The Treasury now confirms it didn't participate. So much for that.