Last slide in this lecture states "Custom SSL must be stored in ACM in US-EAST-1 or you can also store them in IAM using IAM CLI". I don’t think you can store SSL in IAM.
Yeh you can store SSL certs in IAM. This was the way to do it before ACM launched and it still an option if you have a company policy preventing the use of us-east-1. https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_server-certs.html
Also check out the CloudFront console, it clearly states that there are 2 options: ACM in us-east-1 OR IAM.