He is correct that the deregulation of some of the loans was a factor; however, the issue wasn't just offering small house loans to low income folks, but also offering large houses to low and medium income folks. With loans being granted to more and more folks, the prices of houses increased, loans became more and more creative- like pay interest only for the first five years at a 1% rate etc. On top of that, banks and other financial institutions were allowed to invest at a 30-1 ratio or higher, meaning that for every dollar in assets they owned, they could invest 30 dollars. The moment something bad happened, slow economy, bad day at the stock market, housing prices reach their limit- it all came crumbling down like a house of cards.
The writing has been on the wall for years, but people wanted to pretend it wouldn't happen and well folks were greedy- too greedy.