We have heard this for the last 20 years and a double blown is stronger.
What does this mean and is it real?
In a since all almost pipes are double, triple or maybe even 20 times blown. This is how many times a pipe is shrunk and re blown out so the color on the inside gets melted in. This can usually be done in 2-3 times. But it can also be done by a good blower that allowed the glass to get hot enough to be done in 1 blow.
What makes a good inside out spoon is that the inside is smooth like the outside. Whatever it takes to make this happen is what it takes and means nothing other than if it is smooth inside the pipe has been worked properly.