This is quite a slippery slope. If I host a website in one country, I do not necessarily care where people access my website from. It is not like I actively provide a service to them - they just use internet (decentralised network) to access it. What if I publish a newspaper here, someone takes it where the contents are illegal, am I accountable?
> We have been clear that exiting the UK does not allow an organisation to avoid responsibility for any prior infringement of data protection law
In that context it's completely fair to say "leaving doesn't absolve you of past transgressions".
Edit. If Imgur made any revenue from UK users then it becomes impossible to claim plausible deniability on any definition of "providing a service". If the UK can do something about this is a different matter. They could make CEOs/board personally or even criminally liable for the company's failure to pay a fine but probably won't.