Okay, I tested it, and it's completely wrong. You are correct about this one.
Try this, it makes even less sense:
var point_from = Vector2.ZERO
var point_to = Vector2(100, 100)
var angle_to_point = point_from.angle_to_point(point_to)
print("angle to point (100, 100) = ", rad2deg(angle_to_point))
point_to = Vector2(-100, 100)
angle_to_point = point_from.angle_to_point(point_to)
print("angle to point (-100, 100) = ", rad2deg(angle_to_point))