The current version of the report on the auditor's website says the county solicitor said section 213 gave them authority for "an audit or examination of the HCLS’ records that contain information that is relevant to the allegations." The allegation was that the person serving as CEO of HCLS and president of the Board of Tustees was using library funds—which primarily come from county taxpayers—for personal purposes.

The report appears to have been revised since its original release. The current report just says the library didn't cooperate with the investigation. The original report, in addition to the whole stakeout thing (which I'm not defending), said the auditor tried to get access to library records and employees but was rebuffed by the library, with a few more details than the current revision. That's what really struck me when reading the report. According to the auditor, the county's lawyers thought this was reasonable, the county council gave a directive to investigate, and the library just refused to cooperate, at least to the degree the auditor felt was necessary to conduct the investigation. (And then the report started bringing up people's apparent race and clothing. I think I see what they meant, but it's not a great look. I'm going to hazard a guess that no Black people reviewed the report before it was published.)

So some lawyers thought some investigation of the library by the county was legal. The details and methods of access to records and employees might need to go to court to be resolved, but there do seem to be legal arguments to be made in the county's favor. (I don't know what those specific arguments are, since the county solicitor's exact words aren't part of the public record.) If the stakeout was, as some people seem to be characterizing it, the auditor hiding in the bushes at the library, waiting for someone to do something nefarious, that's probably not covered by whatever the solicitor wrote. On the other hand, if the stakeout was, "I drove past the library and there was definitely an event that seemed to be closed to the public," that might be more supportable.