Yes, the transfiguration is celebrated on the 19th. But "Buhe" the chibo burning ceremony is on the evening of the eve.
Yes, the fire is symbol of the light of the transfiguration. Buhe itself means light.
Hoya Hoye is the song children sing as they burn the chibo. The messages of the Hoya Hoye song are directly related to the transfiguration. Tradition says that children/shepherds at bottom of Mt. Tabor were rejoicing and singing at the sight of the light of the transfiguration and that they didn’t even know it was night because of the light and that their parents, knowing that their children were late that night, sent them mulmul or correctly “hibist”.
Therefore, the Buhe is a traditional ceremony depicting what happened at Mt. Tabor.