This is really good question!
As far as I see things,
economy is the same thing as 2 string sweeping,
everything above is only sweeping(3 strings,4 strings etc).
Note,economy is very often mixed with alternate picking,
you do economy just to connect notes on 2 different strings easily,
with less effort for your picking hand,that's why it's called economy.
On the other hand,when you run into sweeping section
you'll probably have few arpeggios to execute,without alternate,
just pure sweeping up and down.
I see. But
here's a lesson that has more than 2 string economy.
But I understand what you are trying to say.
"The rule is to play alternate picking always except when playing two notes on adjacent strings.
Whenever this happens, we will use
sweeping to continue the movement started. "
So that's what was said in the description of
this lesson.
I'm pretty confused right now...