I would take it as a rumor, personally.
The gold reserves of the United States has been a particularly controversial topic through the years for obvious reasons. And talking about using a significant amount of them to buy an asset like Bitcoin will definitely find opposition from the democrat party (which harbors much anti-decentralization sentiments).

It would be more realistic if Trump managed to pass a law which used seized Bitcoin from illegal activities to start to stockpile their own Bitcoin reserve for the ground up.
Even that law would find some level of opposition from the democrat party.