While the blog does use "primary", people are saying "master"/replica, much like how redis refers to their architecture[0]. In fact, ctrl-f "slave" only brings up your comment.
Out of all the comments that use the term "master" as of right now[1-5], the first three specifically use the term "replica" while the 4th and 5th use the verb "replicate" (in the present tense and past-tense).
0: https://redis.io/docs/manual/replication/