Yes, that's about right.
Starting with the basics: You can define "office hours" for the system, which allows you to specify different actions for incoming calls from trunks (or calls to extensions). The designation of a holiday date forces the system to use the "out of office" routing rules for the entire day.
Each inbound routing rule also has a check box labeled "Play Holiday Prompt on Public Holiday". If this is checked, and an incoming call uses this rule, and it is a designated holiday, then the system will play the audio prompt for the holiday (if assigned), then route the call the the "HOL" Digital Receptionist instead of following the "out of office" routing. If you want to have a special holiday menu, you can define the prompt in the HOL Digital Receptionist and menu options. If you just want to play the special prompt assigned to the holiday and transfer to a different IVR menu, then leave the HOL Digital Receptionist prompt blank, set the timeout to 0 and set the timeout destination to another Digital Receptionist.