49 CFR Part 220 Subpart C applies to railroad employees who are members of the operating crew, or anything that would interfere with the safe operation of the train. I personally don't think a non-crew person in the cab shooting video engaged in general chit-chat would interfere with the safe operation of the train. There's plenty of cab ride videos posted.
The issue here is that an "internet expert" made a public claim of a federal violation, though the thread was quickly removed.
Be careful what you say and what you post. I've seen plenty of crews do questionable things but even if I have pix of it I don't blast it all over the internet. The FRA has been known to monitor social media, and that could lead to unintentional consequences (though there are some out there who thrive on causing chaos).