In this context, "new" refers to:

Thus, "indexofwalletdat new" is a search query designed to find recently exposed, unsecured Bitcoin wallet files sitting on public servers.

These are security researchers and "good Samaritans." They run these queries to find exposed wallets, download the file, attempt to verify ownership (e.g., by checking for a contact email in the same directory), and then notify the server administrator or hosting provider. Their goal is to get the file removed before a thief finds it.

Block search engines from indexing your backup folders:

User-agent: *
Disallow: /backups/
Disallow: /wallet/

Remember: robots.txt is a polite request, not a security wall. Never rely on it alone.