IANAL but it seems to be part of the agreement. From the posted pdf:
5.4 Manufacturing sites
AstraZeneca shall use its Best Reasonable Efforts to manufacture the Vaccine at manufacturing sites located within the EU (which, for the purpose of this Section 5.4 only shall include the United Kingdom) (...)
In short, AstraZeneca agreed to use UK facilities to manufacture doses for the EU.
>> The doses that exist in the UK only exist because of a manufacturing ramp up done under their own contract while the EU was still negotiating a lower price.
Presumably, AstraZeneca agreed to provide a certain number (censored in the pdf above) of doses to the EU after AstraZeneca had initiated the "ramp up" you describe. They did not object to selling those doses that were manufacture during the "ramp up" to the EU. The contract doesn't mention any ramp up at all.