There was no talk on the video of an explosion, and it doesn’t look like it was. It really is odd to see most of the building completely in rubble below knee height and parts of it still standing three stories high. Maybe I am seeing a couple of different buildings.
Was listening to someone on one of the live feeds saying they were taking pics yesterday because the building looked so odd, unsafe. Someone was doing brick work. Didn’t catch it all.
The structural engineers will have to get in and look at the details, but an older, lightly-constructed brick building can indeed have a catastrophic failure like this due to deterioration of the supporting structures. And once the framework starts down, the collapse accelerates.
Read this book for details, especially the chapter on the collapse of the Civic Tower in Pavia, Italy - death from old age.