Regardless of the maturity length of the debt instruments the Fed is buying, it is an increase in the money supply unless you're literally defining the money supply to include what the Fed is purchasing.

So yea if U.S. government debt is defined as money, then I guess the U.S. government buying its own debt back with printed money is just "swapping assets". Surely however there are implications of a country indefinitely buying back it's own fiscal debt with printed money, even if they tend to be exaggerated since we're not exactly seeing hyperinflation now.