Bombs are really unpredictable. The assassination plot to kill Adolph Hitler failed when he "miraculously" escaped the bomb, which killed others in the room. The Nazi propaganda machine played it up as a divine miracle of God, evincing proof of divine favor of Der Fuhrer.
If it were the only piece of evidence, you might have a good point, though as I understand it, the image on the other side of the wall was damaged. Whereas Our Lady's image, which was between it and the bomb, was not. Reportedly, the windows in the Church and around the Church were broken too, yet the glass of the image was not, nor was the image damaged.
From my perspective, there is much evidence for the traditional story being basically true. But some difficulties. HOwever, there are difficulties with much or most of what we know to be true, including even the Sacred Scriptures.
As I see it there are a few options here, such as:
--we can say we just don't know what happened, which would leave open the possibility that the miraculous story is essentially correct, as well as the possibility that it was somehow fabricated. This seems sort of convenient, and doesn't seem to respect the evidence mentioned in my last post.
--we can provide an alternate history to the traditional miraculous story. We could say that it was painted by a master painter who for some unknown reason decided to paint the image on a poor surface, and leave the masteriece at Tepeyac. This seems very doubtful, as the master painters agreed in the 1600s and 1700s that nobody could have painted the image. I also don't know how it would account for the facts I mentioned in my last post, including the lack of sizing and the image's durability under bad conditions, handling and kissing, UV and infrared light and smoke from many candles, serious humidity and corrosive air, etc
--or we can suppose that the traditional story is perfectly historically accurate. the biggest problem with this is that there's really no record of the people in Mexico city knowing the miraculous origin of the image until the late 1550s or later (though the natives might have known), though the traditional accounts say all the residents of Mexico City knew about it from the beginning in 1531. The problem with disbelieving this traditional story is: where is the record of people saying that the story has been falsified or embellished?
--or we can suppose that the story is essentially correct, but that it is incorrect about the publicity of the story. That Zummaraga did see the miracle of the roses and saw the tilma, and for this reason approved the chapel. But that he, for some reason chose to not write about it or publicize it (or if he did document it, the document was stolen or destroyed).
--or we can just say that the image is miraculous, but that the story is not so much a history as a symbolic, spiritual representation of what happened. What it does accurately convey is the beautiful and miraculous image, the message of Mary's Motherly love for both natives and Spaniards and her desire for their unity, her desire to console everyone in the chapel at Tepeyace, and the sanctity of her messenger, St. Juan Diego.
I believe in the last options, option 4 and/or option 5