This is hair splitting, because the effect is exactly the same. The UK made sure not to export any vaccines until it has more than enough. This is exactly what the the US is doing, even if they use technically slightly different means.
If the EU had paid for the vaccine's development, they could have had the deal instead.
But they didn't.
And how much would be the EU's "fair" share of vaccine manufactured in the UK? As they seem to be expecting far more than that 25% for themselves, from their retoric they wanted it "evenly" distributed, i.e. massively in their favour, directly from Ms Von der Leyen's mouth:
“That is the message to AstraZeneca, ‘You fulfil your contract with Europe before you start delivering to other countries’.”
There's nothing "fair" about the EU's distribution of the vaccine, claiming otherwise shows complete naivety or bare faced lying.