EX188 is clearly stating "As with all Red Hat performance-based exams, configurations must persist after reboot without intervention." , yet DO188 doesn't cover how to setup podman containers to start on boot. Is that on purpose ?
You're right, it doesn't.
The RH134 course, chapter 13 (part of the RHCSA exam), however, does teach how to make containers persistent.
Part of the prerequisites for the EX188 say, "A Red Hat Certified System Administrator (RHCSA) certification is recommended but not required."
So while it isn't required, it'd be a very good thing to know what's in the RH124/RH134 courses and/or earn the RHCSA (EX200) exam.
"usually RH courses are expected to cover everything needed for the exam"
Most times, they don't. For example, the RH294 course (as the RH254 before it) does not cover many of the required things a test taker needs to know / do during the EX300 (RHCE) exam - things that are covered in the RH124 / RH134 courses and RHCSA exam.