I don't know for sure to be honest. At a guess I think they are initially for emergency purposes to get citizens back to the UK but if you look at the paragraph under the EasyJet photo it says that their flights have now been put on general sale. Whether that includes foreigners I don't know.
Edit: Also the point still stands. It's still gonna be hundreds if not thousands of people flying into the UK every day. Their nationality is pretty irrelevant.
They all have to quarantine for 14 days anyway, and they've all been under very strict quarantine for 3 weeks in Spain.