From looking at Berlin Freepers link it looks unlikely it was a bomb. IMHO a structural flaw is most likely. If you look at the remaining portion where the collapsed section attached it appears to be sagging to the right. Just a WAG: improper piling design.
“Just a WAG: improper piling design”
It appears there are adjacent Apt. Buildings of similar if not exact design. Wondering if everyone will need to vacate for retrofitting?