An incomplete quote from the policy statement is below. I strongly encourage y'all to read the entire article, since there's more conditions than I'm pasting here, but these are the highlights that answer your question.

https://webkit.org/blog/6784/new-video-policies-for-ios/

"<video> elements will be allowed to autoplay without a user gesture if their source media contains no audio tracks."

"<video muted> elements will also be allowed to autoplay without a user gesture."

"If a <video> element gains an audio track or becomes un-muted without a user gesture, playback will pause."

don't need to remove the audio. it's muted by the browser. removing audio just saves bytes.

Incorrect. If an audio track is present, the mp4 does not qualify for autoplay unless other conditions are met.

EDIT: Context is unclear about whether the parent's guidance is about <video> or <img>. No idea what <img> does. I sure hope it doesn't play due to the wasteful audio track, so that people are forced to do it right instead of lazy, though!

in the context of <img> the audio track doesn't play anyway. dropping it ensures you save the bytes.