In HI they call those flower trees plumeria, and it does look like one. Kids do Halloween in HI although IIRC it doesn’t seem as big there (when I was there) as on the mainland.
I don't see anything mysterious about that image, Stanley Armour is shown at the beach with the same child - at about the same age. Doesn't tell us who else was there, or who his parents were.
I’d stake my life on the fact those 2 were not in front of that flower tree for the photo. I am not surprised that the tree is easily recognizable as one that grows in Hawaii. That was the intent.