I'm not really all that bothered.
Okay, if someone is in the door zone and seems to be at risk (however you define risk) and you suggest they might be safer further out, they can either decide that the advice is good and relevant o they can ignore it/decide that its a nonsense.
Its their choice and if the cyclist IS doored after ignoring advice, then you may feel less guilty than if the cyclist is doored and you never offered advice
No-one HAS to take advice
I have no idea whether the cyclist was in the door zone or not, I haven't seen the video and am in no great rush to . It's their choice, just as its my choice to ignore advice (albeit poor advice IN MY OPINION) to use the cycle path instead of the road, and in doing so I am choosing my own destiny