To the extent that one accepts the view that measured inflation should be kept some distance above zero, a very low positive measured rate of inflation (say, 1/2 percent to 1 percent per year) is undesirable and implies a need for highly accommodative monetary policy, just as would be required for outright deflation.
The language of the May 6 statement encompasses the risks of both very low inflation and deflation. I suspect that for the foreseeable future, of the two, the risk of very low but positive inflation is considerably the greater.