Hello Atjaiwo!
Thank you for reading my article and for pointing this out - I was intrigued too as it doesn't seem like there's any other way to merge the tables without using join.
I've checked with Danny on how to solve the question without having to use joins and this was his reply:
"For the danny’s diner - it’s actually supposed to be used with joins, it’s more that “the rest of the team” is not supposed to know SQL so either a derived table or view using the table joins would be ideal ".
What he meant was that Danny (owner of Danny's Diner) and his team would not need to join the tables themselves as we've merged the tables for him and the team.
Hope that clarifies :)