It's not so much a terror thing. It's a demand thing.
When the UK government signs details with Pfizer, or Astra Zeneca or whatever there will be confidentiality clauses. (And AFAIK the UK government is buying for ALL of the UK, not just England),
These vaccines are the most in-demand product in the world at the moment. The UK government don't want it out there how many they've bought, at what price and on what time scale because what's to then stop Russia, Japan, Mexico swooping in, offering twice the price and putting AZ or Pfizer in a difficult position. They will have asked the drugs companies to sign an non-disclosure agreement to that effect.
Then their own devolved administration publishes it online, for every single government in the world to see. What a bunch of amateurs. No wonder Westminster are furious - this could easily have cocked up the entire supply for the whole of the UK and it would be entirely the fault of the Scottish Government.
I think that's what they mean by "security of supply" or similar, about the companies supplying the vaccines in the quantities agreed, rather than about a terror attack. Although again, the vaccine is the most prized commodity on the market at present and i'm sure organised criminal gangs would love to have a few thousand vials to flog on the dark net.
Still a massive cock up.