For what it's worth, layaway isn't common in the US anymore. It's entirely possible they didn't know about it, or don't consider it worth mentioning because the couldn't find an example of a company actually offering it anymore.

The article was written in 2017, and mentions an APR of 19% for a $200 purchase via Affirm. Looking online it looks like their current rates are around 10-13% unless you pick the shortest term loan[1].

[1]: https://www.affirm.com/how-it-works