I assume he was taken to a US airbase and flown from there.
Americans can recall diplomats back to their home country at any time. He was recalled somewhat more hastily than most.
I imagine they said something to the effect of “you will be deported and stand trial in the US; the only question is whether you’re prosecuted in the UK as well”. I imagine that, plus promises to keep his name out of the media, were convincing.
The BBC article goes on with "He was flown back to the United States on a commercial flight, but their investigations are ongoing in conjunction with UK authorities." though.
That's good when the sex offense is for something truly evil.
The problem is the US is a Puritan asylum, so things that'd never register as offenses in sane countries, sexual or otherwise, can get people's names in that registry, destroying their lives.
And several States are weaponizing this by expanding what's legally labeled as sexually offensive so it covers harmless behaviors of minorities, so now there are people under risk of getting included in the registry due basically to existing.
Americans can recall diplomats back to their home country at any time. He was recalled somewhat more hastily than most.
I imagine they said something to the effect of “you will be deported and stand trial in the US; the only question is whether you’re prosecuted in the UK as well”. I imagine that, plus promises to keep his name out of the media, were convincing.