The author is concerned that an ad might be able to surreptitiously turn on the camera or microphone, but these are not accessible by default. In this case, it isn't even getting as far as a permissions prompt because the default Feature Policy doesn't allow camera or mic access in cross-origin iframes. (Ex, for Chrome:
https://sites.google.com/a/chromium.org/dev/Home/chromium-se...) Instead, I think the most likely thing happening here is that an advertiser is running a script that is trying to do fingerprinting, and which is blocked by the browser protection.
(That it's an iframe running on https://[random].safeframe.googlesyndication.com tells us it's an ad served through Google Ad Manager, and the contents of the iframe are supplied by the advertiser.)
Disclosure: I work for Google, speaking only for myself