Ryan says the certs for CF are separate from LB’s. This is not true. He does clear it up a bit by saying they are separate copies.
When this lecture is updated it would help to discuss how the CF dist certs use ACM like all other ACM-compatible AWS services. All of them ingest a copy of the same, centralized, cert.
I have submitted your suggestion to the content team for consideration.
It might be worth noting that CF public certs (for content distribution) are sourced from ACM in US East (N. Virginia) only. Certificates used to secure backend traffic to your origins can be sourced from ACM in any region.