If you want to understand it in detail, look it up on google. First off WTC 7 was not built as a normal skyscraper, it's bottom was essentially "hollow" meaning that it was not strongly supported. When the towers collapsed the debris rained down on WTC7 taking out a huge chunk of the the bottom of WTC7(which there are pictures of), furthermore WTC7 burned for about eight hours(the fires were fueled by the back-up diesel generators), which also weakened the infrastructure of a building. In conclusion, WTC7's infrastructure was severely damaged by falling debris and the eight hour fires that ensued. And when you take out the essential infrastructure of a building it collapsed "like a deck of cards". That's why it look very similar to a "demolition", because in a demolition they take out the essential infrastructure, they don't blow up the entire building.