There's no mention of that in the article so no idea.
Found another article that said the UK had donated doses in August that were due to expire in September which would seem to indicate that donating the 600K in question back in May with an expiry of August wouldn't have been an issue but if the rules say otherwise then that's obviously why they were binned.
On top of bureaucratic hurdles, there is also the issue of limited shelf life. COVAX generally only accepts doses with at least two months left before expiry. Vaccines nearing their use-by date can end up being destroyed, as happened with 385,000 doses delivered by COVAX thrown away between June and September 24, according to a document seen by
POLITICO.
The concern around shelf life links to yet another conundrum: COVAX has been loath to receive doses directly from countries, stranding shots in EU warehouses. While it’s technically possible for EU countries to donate doses already handed over by the manufacturer, the threat to the integrity of the cold chain and expiry date concerns make this “very difficult to do,” said the development official.