If a particle has no charge, then it is possible for it to be its own antiparticle, but it is not necessarily so. [....] The neutron, on the other hand, is neut

If a particle has no charge, then it is possible for it to be its own antiparticle, but it is not necessarily so. [....] The neutron, on the other hand, is neutral but is distinct from the antineutron. The neutron is only electrically neutral, there are also weak isospin and color charge. Antimatter is not only concerned with electrical charge but with charges in general. In case of the neutron and antineutron this becomes obvious if you compare the quark content of both.