"Are you saying the confusion was that we weren't clear between M365 and O365, or that we just said Microsoft E5 rather than Microsoft 365 E5?"
Yes. 
1: There are a lot of services and suites - it's ideal to always be explicit if you mean "Microsoft 365 E5", particularly now with the (confusing, IMHO) rebranding of many Office 365 services/features as "Microsoft 365" - especially since there's no "Microsoft E5" suite.
2: A lot of customers - whether it works out ideally or not in the end, license things on an à la carte basis rather than as whole suites. So for things like this, which would appear to require subscriptions to Microsoft 365 Apps for enterprise (the artist formerly known as Office 365 ProPlus), Power BI Pro, and
Azure Information Protection Premium (P2? P1?), it is really useful for customers if you can define what licensing is necessary in order for a feature to be available (or even just licensed correctly, as so many things don't do comprehensive license enforcement anymore).
Thanks!