Had a humbling moment 3 years ago when I realized I'd been holding my taping knife wrong the whole time.
At a job in Tucson last week, a guy my age showed me a 6-inch taping trick that cut my corner time by half, and it made me wonder how many other bad habits I picked up from just rushing through early jobs.
Your buddy mixing mud backwards doesn't really matter though. I've dumped powder first for twenty years and a drill with a paddle mixer handles lumps just fine.
My buddy Kyle spent two years drywalling basements before somebody at a job site finally told him he was mixing mud wrong. He was dumping powder in first then adding water, which made it lumpy every single time. The whole crew just watched him struggle for months cuz they thought he knew what he was doing. He said he felt like an idiot but honestly it happens to all of us when you're just trying to get shit done.