To Speedbump:
Yes, I have been thinking along the same lines as you, that is what makes this such an interesting case.
I really would love to know how they decided upon this approach. I am especially curious about the "plug from outside" technology. There are many pros to have a plug inserted from inside - especially in an airplane.
Plug from inside would require a sharp angle scarf joint (or something with these pegs, nibs, hooks etc) though, otherwise the material might weaken in the edges, enough to MAYBE compromise the plug enough to make it fail catastrophically. A blunt angle scarf joint (which is, I believe, the case with this plane) could theoretically vibrate the glue enough over time to make it unstable.
Now they plugged it from outside. The theoretical case with the glue still stands but they removed the feature for the plug to "plug itself" into the hole. Speculating here, maybe that is to reduce compression stress on the glue. This would correlate well with the patch from inside that supposedly could reduce the effects of pressurisation (which would cause a tension stress on the glue), thus trying to keep glue properties stable. Just speculation from my side.
Thoughts on this?