Hi Brad,
A custom registration field can be follow type:
·Simple Text
·Boolean(Yes/No)
·Single Choice
·Multiple Choice
If invitee populate this type of field, it will generate record called Registration response.
For your example yes/no, it's a boolean type customer registration field.
Now I add such field to my event page.

Obviously a response record with anwser Yes will be generated.

And also for No.
However, I met an issue in my environment that response record with anwser No won't be generated if I not check the field at first name, only when I check and then uncheck the field will also generate No type records.
Now I found a more effective way to filter out contacts from registration, which not requires we add custom registration field to event form.
A field called Originating event in Contact entity could be identifier/flag what we want. If a contact has registration event, this field will contains data.
So I add a view(Contacts with registration view) for contact entity in customization with filter criteria in screenshot below:

Then all contacts that have event registration record will be filtered out, we can either see their registrated event in this view.

Regards,
Clofly