Les, obviously additional ingredients need to be added to the meat and mixed through adequately. I think the video cook was more so referring to the formation of the meatball and then the compaction of this into the pattie shape. Too much attention here is the likely cause of the shrinkage.
I remember back to my youth and late nights at the pub, when drinks were over at 10.00 pm. Many patrons would cross over the road to the packed out burger shop, affectionately known as "Greasy Ray's" back then. If memory serves me, Ray's patties were actually large round meatballs and he didn't flatten them till they hit the grill plate and he adeptly spread them out using 2 large spatulas. His charming wife, Lizzy was not to be crossed and she kept control of the often near riotous crowd by simply threatening to deny food to trouble makers. This usually, but not always, worked.
Since watching that video and for uniformity of shape I use a double egg ring and simply push the meat in, run a knife around it to remove the ring and that's it.