At best, the natives would be concerned and frightened. At worst, suspicious and angry.

The investigator would most likely be left on the isle, since something obviously went wrong somehow, or the gods were angry with this foundling.

The exception would be if the wound looked super fresh (as if the foundling had just had a tangle with a needle-fish or something). In that case, there would be pressure to go back to the Gods on the Day of farewell, but the foundling would be cared for in the meantime.