It's utter nonsense.
It relies on your being too busy to read Article XXIV of the GATT, or too confused by trade legalese to parse it.
wto.org/english/tratop…
Article XXIV doesn't oblige anyone to do anything.
It's there to allow Members who have reached an agreement between themselves to form a Customs Union or Free Trade Area to do so, or move towards doing so.
It's entirely irrelevant.
The EU and UK are nowhere near agreeing a new permanent Customs Union. nor do they have an interim agreement or implementation plan to present to the Membership. Even if they did, Russia or someone would likely block.
Merry MFN Christmas, ya'll.