This Druid is a messenger from the Druid Grove sent to inform the party that any party member who is a druid and has reached Level 14 is expected to return to the Grove and challenge the current Great Druid for the title of Great Druid. He'll then leave and disappear.
This sets off a timer of three days in which the party must return to the cave in the Druid Grove. If more than three days elapses the messenger will return and remind the druid in the party of its responsibility to perform the ritual.