Right now it's extremely restrictive and silly. Because it's presuming what will be most helpful for the assistant without knowing the context of how the assistant is engaging with an end-user.
Also there's no details within the UI that states that the assistant will
randomly
select from the array of strings that is to be the response to be said upon silence.
It confuses the user/developer (us).
Idle messages can be described instead as: "What do you want the assistant to say to break the silence if there is one?"
"How long should the assistant wait, before breaking the silence?"
Etc. Lots of descriptions are too "technically" oriented it's not helpful nor is it tailored to those who may be using the assistant to create value for the end-user. Just an opinion.