The thinner material in a butted tube does sound different when given the finger nail tap. If you don't hear a difference, your tube isn't butted.

A tried and true test shown to me by a bike mechanic back in the early 70s.

A tube can have multiple wall thicknesses in it, making it multiple butted. Were they better than double butted? I have a quad butted Fuji, I'm sure it's a bit lighter than an identical size frame made with identical tubing that was double butted instead, but I doubt it's better.

Pose this question in CnV and see what answers you get.