I find that contractors don't take decks seriously. If they don't follow your details, they say "why are you so concerned with just a deck". It is usually the connection into the building that is the issue. Decks can be design to be as safe as any other portion of the building. It is just that they aren't designed or built well.
This appears to be a drip through deck (there is no membrane and water can drip through the deck) with a soffit. This is not great since the rain water goes through the deck but the soffit help retain the water. One thing this deck had going for it was the roof over which would have minimized the exposure to rain. Good practice is to avoid drip through decks that are supporting a portion of the building such as this case. Although the roof protects the deck, it is not a great idea to rely on the drip through deck to support the roof. I am also not a fan of multilevel drip through decks.
From the photos on google, it looks like the joist were running parallel to the facade which is unusual. I couldn't see any connections for the beams into the building. There should be beams at the column locations.
One report said that this was a pancake type failure. Another witness said the first level came down first and the other level came down slowly. This contradicts the claim that this was a pancake failure.
There doesn't appear to be much damage to the facade of the building. Glass and siding are not broken or ripped away from the face. However, the connection to the building does not appear to be substantial. The other possibility is that the one witness was correct. The fist suspended level failed first, the columns were pushed outward and then the upper level was pulled out.