That link does not say a word about immunity
Correct. But it was used as a kind of a "passport" (maybe not mentioned in that article, but I recall seeing elsewhere that there was green or red to allow entrance on public transportation and IINM also malls), and I honestly think that there's no escaping some sort of "immunity passport" to allow a return to functioning societies and economies.
That being said, with the news of the Oxford vaccine having the best results with 2 doses, it would lend to reason that a recently recovered COVID-19 person might gain greater immunity if exposed again.