Your reference article says if more than 3/32" to replace all four. My story involved 1/32". Little bit of a difference huh? Maybe the service manager could have explained it better? He still would have been wrong at 1/32" though.
Correct but the problem also gets added to when you remember that tire manufacturers have started widescale manufacturing in china, leading to out of spec tires coming into the market, so one from a few years prior would measure different, or the OE spec tire (assuming that's what was on it? Or whatever tire it had) could have been discontinued making it so the new tire may "measure" the same but have an actual dimension that could put things out of spec.
I worked in a tire shop when some of our suppliers switched to overseas factories we had A LOT of out of spec, out of round, bad dimension, wouldn't balance tires that were the 'same' as the US made ones that were much better