You probably got a free Switch. And with their subsequent behaviour, a well deserved one.
US seems to just have a more broad term for goods delivered that you didn't order and refers to it as "unordered merchandise"[1]. You're pretty much free to keep it, it seems.
The UK is more specific for what is classified as "unsolicited" and what is considered goods delivered to someone else by mistake[2]. Companies have a right to get their product back if it's the latter. Since the author did order a switch, a duplicate delivery would very likely be considered a mistake. If the author never ordered a Switch (and never paid for it) in the first place, they'd definitely be able to keep it.
Regardless, if this is the way Nintendo asked for the second Switch back, they were completely out of line.
[1] https://www.consumer.ftc.gov/articles/0181-unordered-merchan...
[2] https://www.saga.co.uk/magazine/money/spending/consumer-righ...
If the law is similar in the UK, Nintendo is mostly in the right. However, I don't think they have the right to ask the guy to be at home at a time of their choice.
Most countries have laws regarding that practice, but the details can be very different.
That said, if the seller makes a mistake then they need to rectify it entirely, they can't demand you wait around for a courier at an inconvenient time or get you to pay for postage.