Nintendo nor any other company would admit they used scarcity marketing in the past or using it now. So quoting what ninty says isn't very relevent. It's just the kind of pr that goes along with it. Owning up to the practice would defeat the point of it and consumers generally don't like it. It's a smart business strategy but it has some risks.
In response to your questions, you can't distinguish between the two just from one instance (like looking just at the switch because you can easily say it's due to supply contraints, etc) but you can tell the difference if it's obvious, something is leaked or if it's done enough to form a pattern. In ninty's case, they've done it enough to show a pattern if you look at past shortages with their other products and you're just honest with yourself about it.
Does this methodology you describe eliminate the possibility that Nintendo is just terrible at anticipating demand or perhaps external factors have come into play like a NAND shortage?
A number of outlets are reporting or have reported on NAND shortages:
And Nintendo needs these components to assemble Switch units. They're competing with smart phones:
So if you're looking to place blame for Switch shortages on a conspiracy theory, please understand that a shortage can have multiple causes. In the Switch's case, a NAND shortage or Nintendo's inability to anticipate runaway demand.
Unless, like Curl-6 stated, Toshiba and smartphone makers are in on the conspiracy too to limit the supply of Nintendo Switch units out on store shelves.
So if Nintendo's lying about shortages, what about Toshiba, and all the other sources citing the scarcity of components like NAND memory? Is it all some vast industry-wide conspiracy to make Switch look popular? That's entering tinfoil hat territory.