Yes.  The timescale of FRBs is too short to be caused by mergers of supermassive black holes.  In general the source of an event cannot be any larger than the time for light to cross the source.  In the case of a supermassive black hole binary the light crossing time is of order seconds to minutes, but FRBs last for only a few milliseconds.  This limits them to be the size of neutron stars or smaller.