Kafka Streams are also amazing, and would have solved many problems I've encountered in the past better than our microservices moving data around themselves.
Would you mind expanding the use cases you would have used Kafka streams for? And why no other solutions could have helped? (Performance or complexity etc)
Where did that idea come from? He literally wrote how they did it without streams by moving data between their Microservices, likely with synchronous http calls. He would've just preferred to just write a stream instead of the services.