Sherm,

Indeed, the funds do not belong to the U.S. Government, they belong to the Venezuelan government.

They were frozen in place (i.e. in bank or investment accounts in the name or for the benefit of the Venezuelan government at financial institutions in the U.S.) by Executive Order and became protected assets under the authority of the Treasury Department (OFAC). The U.S. Government can release the frozen funds to the Venezuelan Government recognized by the State Department as such (Guido's in this case) upon petition by the Venezuelan Government for legitimate purposes.

The frozen funds are released to the owner upon U.S. Government approval (The President or the Treasury Secretary), which is followed by an authorization issued by OFAC to the financial institutions holding the funds to release them at the owner's request.  

In fact, President Obama authorized the release of the Iranian frozen funds ($11 billion) once the foreign relations between the U.S. and Iran were normalized after the nuclear weapons deal (which was later cancelled unilaterally by President Trump).