From the Firebase Security Rules

CodePudding user response：

You are right: The rules in your question, which check custom claims, don’t incur Firestore reads.

It is most probably a copy/paste error in the documentation: If you look at the doc page, the block above the one you pasted in your question has the exact same sentence (and this time this sentence correctly applies to the code example, which includes the get() function).

(FYI I’ve used the feedback button at the bottom of the doc page to report the problem to the Firebase team)