How to distinguish between ContentDocument and ContentNote?

There seems to be some unusual stuff going on with SObjectType for the enhanced note ContentNote (ERD) object and the underling ContentDocument (ERD) structure.

For example, both these return a single row (with the Id taken from an enhanced note I created);

select Id from ContentDocument where Id = '069R00000002J0m'
select Id from ContentNote where Id = '069R00000002J0m'

and these both return “069”:

System.debug(Schema.getGlobalDescribe().get('ContentDocument').getDescribe().getKeyPrefix());
System.debug(Schema.getGlobalDescribe().get('ContentNote').getDescribe().getKeyPrefix());

and this:

System.debug(((Id) '069R00000002J0m').getSObjectType());

outputs ContentDocument.

This turns out to be quite awkward for a change to some existing code that I am making, in that AFAIK the only way to generically identify an enhanced note versus a File attachment is to check that the ContentDocument.FileType has the value “SNOTE”. As far as triggers and SObjectType based logic is concerned, ContentDocument is the type.

Please share any insight you may have on what is going on here so that I make my code changes in the cleanest way.

if(rec.get('LatestPublishedVersionId')==null){
   //Its a Note
}else{
  //Its content document.
}