Censys expands queries to provide additional functionality. For example, the query a:zmap.io
executes a DNS lookup and expands to ip:126.96.36.199.
Your query was changed from:
(tags:oracle) AND 1521.oracle.banner.nsn_service_versions.Authentication: "188.8.131.52.0"
If this isn't what you intended, you can run your raw query without expansion.