In the diagram showing a multi-homed EC2 instance with multiple ENIs, the video states that each subnet is in a different AZ. This is not possible. ENIs are AZ bound and must be in the same AZ as the instance it attaches to.
Reference: Point 3 in Best Practices http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html#best-practices-for-configuring-network-interfaces
That is true. "You can attach a network interface in one subnet to an instance in another subnet in the same VPC; however, both the network interface and the instance must reside in the same Availability Zone.". Hope the instructor clarifies or corrects the lesson to avoid wrong info.