"A resonant state unbound to neutron decay by at least 100 keV was identified" Could you guys please explain this clearly?

Does it mean that If we provide 100 KeV energy to the nucleus in that resonant state then it will decay through a neutron emission

No, it means that there is an enhancement at 100KeV invariant mass when a neutron is scattered from the nucleus, i.e. the energy carried by the neutron is positive, as it is called unbound. See this article in wikipedia for quantum mechanical resonances. This article gives the math.