Andy - yes you're right.
Snapping the neck is the most painless way to kill fowl.
The pictures of the birds struggling to walk is awful, but my suspicion is the men were killing the ducks that had some sort of health issues (like those ones shown struggling to walk) rather than random killings.
Raising fowl it's inevitable you will get some who are not healthy (and would have died in the wild of starvation).
It's the reality of farming that you don't raise non viable livestock.
You have to remember that videos like this are edited to show a position that the organisation putting them out wants you to see. I also note this was filmed over a number of months and edited together rather than 5 mins of continuous footage.
I'm saying this as someone who always buys meat from certified welfare sources or better still local farmers I know personally.
As a family we are are also actively reducing our meat consumption.
However, I didn't see this as evidence of cruelty tbh - rather the realities of farming animals and you have to decide if you're ok with that or not.
In terms of the latter then perhaps the Vegan topics are for you (because if think hens who can no longer lay eggs or cows that don't produce milk go in to a happy retirement in a field then you're mistaken).