"Evidence" has never been limited to the subject of a warrant. Destruction of evidence statutes typically include material that is subject to a police investigation.
An ”investigation” is just a fancy word that broadly describes the type of information collection that law enforcement does. Yes, it is typically about things they think are crimes. Because that’s their job. But there’s not some legal hurdle they have to pass here, the word describes their work.
instead they are harassing
If someone accuses you of a crime, committing a different crime is probably not a good move, in any situation.