Watching the video, it appears to be concrete failure in the structure itself. Foundations typically don’t have catastrophic failure. Say there was a limestone cavern that collapsed deep, a portion of the foundation settles, load flows through the structure to redistribute the load elsewhere other foundation elements. You would see the structure sagging over the failed element. I guess there could be a cavern large enough to have a big void open up below, but not typically in Miami. Tampa maybe
I agree with Kimble. This is likely related to corrosion in one of the structural elements or maybe even a latent defect. Corrosion weakens the reinforcing over time, eventually you lose capacity to support the load. You lose a lower level transfer beam, or the support condition of one of the columns changed (I.e. failure of a beam that provides lateral support to the column) and you get an overloaded column and it explodes and everything follows.
Feels bad though for the families involved.