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?
It's not about "hosting a website", it's about providing services.
If you provide services, like selling a newspaper, in the UK, you need to respect their laws, or you will suffer the legal implications of not doing so.
And regarding the accountability, it refers to the fact that imgur USED TO provide services in the UK:
> We have been clear that exiting the UK does not allow an organisation to avoid responsibility for any prior infringement of data protection law, and our investigation remains ongoing.
Companies providing services outside the UK can infringe all the UK laws they want, the UK doesn't care.
But as soon as you decide to provide services in the UK, you have to follow the law. And, as they explain in the article, if you break the law, stopping to provide services in the UK will not absolve you for your past wrongdoings.