What does the parietal relic of Sakyamuni Buddha mean?

Usually, relics refer to those things left by Buddhism when people are cremated after death. But the bones of some monks will be provided as relics. The parietal relic of Sakyamuni is the skull of the Buddha. But that's unlikely. The only Sakyamuni relic in China is the real finger bone relic of Sakyamuni unearthed in the underground palace of Famen Temple, which is confirmed to be true!