Censys expands queries to provide additional functionality. For example, the query a:zmap.io
executes a DNS lookup and expands to ip:184.108.40.206.
Your query was changed from:
((cam.ac.uk) AND parsed.issuer.organization.raw: "Cloudflare, Inc.") AND tags.raw: "unexpired"
If this isn't what you intended, you can run your raw query without expansion.