In the lecture towards the end, there is mention of KMS ‘keypair'(at arround the 8 minute mark) and importing ‘public key’ via the KMS BYOK (External key) option. Is that factually correct? I believe it should be symmetric keys, KMS does not support keypairs.
Yes, this lecture correct. It is referring to importing asymmetric SSH keys onto an EC2 instance for authentication.
You are correct that KMS does not support asymmetric keys. https://docs.aws.amazon.com/kms/latest/developerguide/crypto-intro.html