Delayed electron emission from superhot neutral C-60 was found to strongly depend on the initial molecular thermal energy. This dependence is clearly demonstrated by measurements of delayed ionization efficiency curves following electron impact for widely different C-60 average vibrational energies in the range of 8-14 eV. These measurements provide direct experimental evidence for the thermal nature of delayed ionization of superhot clusters. A simulation based on decay kinetics with thermal rate constants was found to be in good agreement with experiment.