Ok, your friend doesn't know what he's doing. Almost everyone in the gym is in the same ignorant boat including the trainers for hire. Actually almost all of BBing and commercial gym culture has been in the dark for almost 30 years and pretty much since aesthetics/cosmetics and BBing split from performance and strength training and was able to rely on being able to circumvent horrible training stimulus with enough drugs to still make progress. This is why people are going nowhere over the mid to long term and everyone thinks back to the glorious newbie gains where everything worked and it took no planning to add weight to the bar workout to workout. And this is why people are always changing up their exercises so they can get that same cherry high of easily adding weight to the bar because they are playing with the illusions of deacclimation/reacclimation with no real fundamental progress over the longer term. This is also why so many people are able to sell golden programs based on largely false information and people are so desperate to find that missing link that will transform their blah blah training into a mega mass builder. You must improve your big lifts, you must eat to move the scale. It is not so easy as going in and doing some random crap on different days but it isn't exactly hard either.