That's the worst advice any detector prospector could ever hear. As you've noted, follow it at your peril.I choose to dig all now, as can’t always tell if metal, lead or gold. (Sadly in my earlier usage I was advised to learn which was metal and which was gold and then walk on. Must have walked away from a lot of good gold )
Gold occurs in every possible size, shape, angle in relation to coil, proximity to other metals/mineralised ground, purity, mixture with minerals such as ironstone and manganese, etc, etc. Digging to isolate the target, followed by positive, visual ID, is the ONLY way to be sure what a detector signal is really telling you.
Many years ago I was detecting my way up a goat track to an old mineshaft at Wedderburn in the Golden Triangle, when my VLF detector gave a loud honk through the headphones. I looked down and saw a brown/grey rock on the surface, cursed "yet another damn hot rock" and hit it with my pick in anger. It split open to reveal a golden core like the yoke of an egg! Specific gravity testing showed 52g of contained gold, with fine stringers actually on the surface, but invisible in the dust when I first saw it.