Don't want to be the devil's advocate here but just because camera is on doesn't mean anything is being recorded. As an iOS developer who worked with apps that access camera frequently, I can confidently say that it's just a UX optimization. Starting the camera takes a brief few hundred milliseconds which is easily noticable from a user perspective. By keeping the camera ready, they are making the experience smoother…
Sounds like iOS's fault for not providing a way to keep the camera on standby at the expense of battery life, without compromising privacy. Just like how there should be more privacy-preserving methods for querying clipboard contents, as in the similar TikTok scandal when a UX optimisation was mistaken for a data collection issue.
iOS doesn't really like providing APIs like that.