Not an angel -- a ghost.
Friend of mine was riding a twisty road in the mountains, fairly cold night, when this guy walked past her in the other direction, not really dressed for the weather, his feet not really touching the ground, with a strange blissful look of wonder on his face. A mile or two later she came upon the motorcycle accident scene where that guy had just died. What she saw was his spirit released.
Something like that I suspect.
Perhaps the voice was that of the driver uttered before she died, put out with such force on the Universal Subconscious that it became a viable thoughtform and was able to echo for as long as needed -- at least as long as the child was still alive.