It's true that those two audits aren't the same thing. However, the SOC2 auditor confirms, in the published report, that Tailscale has regular and ongoing security audits including penetration tests and many kinds of code reviews.
The security audit report, which you perhaps imagine to be a long list of vulnerabilities... doesn't look like that. It says we don't have a long list of vulnerabilities. The security bulletins are all here: https://tailscale.com/security-bulletins