My understanding is that the point of microservices isn't to just move what would have been a relational join in SQL to an equivalent join in the service layer, which is what the author is implying. Instead, the order service should already have the subset of user data it needs to perform its function. If a user name changes, for example, that would trigger an event that gets consumed by a handler in the order domain. You embrace some denormalization and duplication of data in order for each service to have as much of what it needs to perform its function without a ton of other dependencies.

I'm not saying this is necessarily the way to go, I'm just saying that this is my reading of the microservices design pattern.