As someone who often speaks gibberish to myself due to ptsd, if someone recorded me in my room they could convince anyone I am utterly insane, beyond any hope. It is a great way to blackmail people with coprolalia or other verbal tics.

And yeah, if they had access to my webcam, they would just see a guy staring into the screen or walking back and forth in the room.

Eh, random utterances are more common than you think. Especially amongst older people. Most will know at least a couple family members who tend to mutter random things to themselves.

Nobody who is themselves sane is going to judge another for random crap they say when they think themselves alone.