Twitter no longer let anyone claim any inactive accounts. And only honour Trademark based claims if it's obvious there was intent to confuse and it's causing confusion.
I have seen at least two instances of Twitter staff taking old, unused short handles after being hired there. But I don't know about the specific policy decision you seem to be referencing (and I don't know whether that decision exists).
Twitter no longer publicly allows anyone to claim inactive accounts. Informally, Twitter employees (and friends of employees) still have channels they can use to claim inactive accounts.