This issue is the failure to latch the three latches on the bottom of the engine nacelle, each of which is capable of holding the cowling closed for an entire flight. These latches are supposed to be inspected each time they are used and if they are not latched they will not be flush with the nacelle and should be caught by whichever pilot does the walk-around.

So no, the most plausible conclusion is not a structural failure but that maintenance opened the cowling and then failed to properly latch it and that was not caught by the pilot who did the walk-around.