Absolutely. The video is at best misjudged and at worst totally irresponsible.
Whilst it can’t be denied that - generally - heritage railways maintain a better kinematic envelope than the mainline, that doesn’t make ‘window hanging’ safe - or even less unsafe, imo.
This is something that the ORR are - rightly - paying very keen attention to, along with the heritage sector as a whole following several
high profile incidents (there are plenty more) in recent years. It is something that is ‘tolerated’ in the heritage sector rather than expressly allowed, and all it takes is one injury and that tolerance will disappear. It is - unfortunately - almost impossible to mitigate the risk of serious injury or death from window hanging (as it extends far beyond simply being bashed) and as heritage lines are required to have a Safety Management System and comply fully* with the Rail and Other Guided Transport Systems (Safety) Regulations 2006 (ROGS) it is very easy to shut down railways not appropriately dealing with the risk - or indeed actively promoting window hanging - by way of prohibition notices. I know for a fact that at least two organisations have had formal warnings (I won’t say who or where) from the ORR about allowing body parts to protrude outside of vehicles.
If I was one of the lines mentioned I’d be asking the person to remove the video ASAP for my own protection, but sadly many faux influencers don’t really have a clue about either what they’re talking about or the consequences of their actions.