This is what I mean when I say scarf join:
Obviously Boeing would use something more like length = 15 times thickness or so.
But there are many other types of scarf joins, some that looks like steps and they can be with or without "pegs" going through the material (no such join shown in this pic but often used in wood):
And here is one that has small "steps" where the join overlaps and creates a thicker material over the join. Maybe this happened to the glider. I do not find it credible that Boeing would use this method on the 787 though.
