Nope, it's a phrase used jokingly by some locals...
It's being trialled in the event of a no-deal, and during a transition period to 'third country' status.
(No-one as yet knows exactly what visa requirements/stay period will be in the event of a no-deal)
Can they do that, unilaterally?
Of course...
Asfaik so far Germany, France, Italy, Netherlands, EEA countries not in the EU (Iceland, Norway and Lichtenstein) have unilaterally offered bi-lateral citizen agreements.
(Don't forget the EU/EEA as a whole did it long ago, but the UK doesn't want freedom of movement even for existing residents!)
These don't of course offer the exact same things as UK citizens currently hold (such as stated the freedom of movement between EU/EEA states) but guarantees someone who has made a life abroad can stay.
Of course there are still unknowns, such as how long you are allowed to be outside the country you have the right to remain in before you lose that right.
Other current rights such as healthcare, pensions etc are in most of those offers but subject to EU/EEA rules given a no-deal scenario.
Also asfaik, the UK has said it would welcome such deals, but won't sign because the UK will not give firm commitments as to who will be eligible to stay in the UK in a no-deal scenario beyond certain guarantees for those in the UK for over 5 years. (cut off dates, period of residency, proof of residency etc)
Hence the impasse for what is being termed 'administrative arrangements' to be agreed.