There is a set of mounting holes on the back of the washer and dryer. Each brand has a slightly different configuration for the holes and each sell their own mounting kits.
https://www.amazon.ca/Whirlpool-8572...70556791&psc=1
The above is whirlpool one which the metal piece clips to a ridge on one piece and screws into the other. The rest of the kits are just some foam with adhesive on it do reduce aliding and dampen vibration.
So is what the saws guy is telling you wrong? Sort of. Brands don’t change mounting between every model and every year. I checked on my LG, The washer went 3 years ago and the dryer went this year and this years dryer would still stack with the same kit despite being a newer model. Now if your on the first part of the switch with a 10 year old dryer and a new washer it might on fit.
But even if the part doesnt fit a handy person could fab something up that would join the two units together in a similar manner to the actual kits.