Speaking from experience, assuming this kid was on the spectrum, getting them to stop shouting or saying something is usually easier said than done, especially if they're in the middle of a fear response cycle, like it sounds like was the case here. It's basically like having a bigger, much more verbal toddler in the middle of a meltdown; there is no reasoning, just an attempt at containment. Believe me, I've clamped my hand over my brother's mouth before in an attempt to get him to stop saying inappropriate things...it unfortunately doesn't work; he just gets mad at me and then repeats what he was saying.
On a not-inappropriate but just annoying note, yesterday he talked about parking garages for twenty minutes straight. I don't think I want to see or hear about parking garages ever again.
I would have been more concerned about the kicking of the seat and watching stuff without earbuds had I been this kid's caregiver. That's the not-okay part.