Customer focus is critical to succeed with management improvement efforts. Few argue with that point, though my experience as a customer provides plenty of examples of poor systems performance on providing customer value (usability, managing the value stream well, etc.).
At times people get into discussion about what counts as a customer. Are customers only those who pay you money for a product or service? What about internal customers? What about users that don’t pay you, but use your product (bought from an intermediary)? What about users that use a service you provide for free (in order to make money in another way, perhaps advertising)? What about “internal customers” those inside your organization without any payment involved in the process?
I find it perfectly fine to think of all these as customers of slightly different flavors. What is important is providing what each needs. Calling those that actually use what you create users is fine, but I think it often just confuses people rather than adding clarity, but if it works in your organization fine.
To me the most important customer focus is on the end users: those that derive value from what your organization provides. If there is confusion between various customer groups it may be helpful to use terms like end user, but really using the term customer for a wide range or customers is fine (and modification such as internal customer to provide some clarity).