This is what the REAL U.S. Treasury department says:
Scammers Falsely Purporting to be Calling from the Treasury Office of Inspector General, Office of Investigations; the Treasury Office of Legal Affairs or Emailing from the Office of the Secretary of The Treasury:
Scammers call an individual asserting that the individual has been awarded a grant or a similar sum of money and request personal information or a sum of money to “release” the funds. The Treasury does not have such a program.
Likewise, e-mails promising a sum of money and purporting to be from the Treasury Secretary or his staff are false. We urge recipients of such calls or e-mails to be extremely wary of any scheme requiring an advance payment for a later promise of funds—these are hallmarks of scams.
(This scammer is generous. He says that the grant is $150,000. The "standard" scammer offers a nonexistent grant between $4,000 and $15,000. Maybe he thinks that a bigger amount will make people act before they think.)