Correct. Note that the next Bookends update (12.8.1) will introduce an updated database engine and some refactoring of the database schema -- your search will no longer work. When using 12.8.1 and later you can use a similar search to the one you have, like this
Locate('Anonymous', attachments) > 0
This is fine, but it will match substrings as well (e.g. it will match this (fake) word 'Nonanonymous')
If you want a search that is case insensitive (like locate) and only matches full pdf names, you can use this (this is how you'd do it in our SQL search box):