(A) Concern about rising interest rates makes perfect sense, as the economy described is in a situation of overheating: high inflation, low unemployment and high economic growth. Rising inflation is a risk that requires the Fed to act to cool economic activity. This should be done through restrictive monetary policy instruments: raising interest rates and decreasing the monetary base, through the sale of government bonds and / or by increasing the banks' compulsory deposit with the Fed.
(B) This affects the credibility of the Fed, which is very bad. Economic agents base their expectations on Fed signals. If the money supply is higher than expected, real inflation will be higher than projected inflation. So expectations anchored in Fed forecasts will be dashed. This makes economic agents distrust future Fed projections.