So he sent an email to the tax department rather than the immigration department, and thinks that their response back was related to his legal status as an immigrant, rather than regarding his tax status.

The guy is an idiot, had literal years to get this dealt with

There’s nothing in the article suggesting any of the people facing deportation voted in favour of brexit, is there? This doesn’t feel like LAMF.

But the tone of all the people quoted in the article… holy shit. Big “these rules should not apply to British people” energy.

Looks like he just didn't ask the right people the right questions and made assumptions, eg asking the tax office about immigration rules and, because it's a government department, thinking that was enough. A tax department does not make immigration rules unsurprisingly to most, except this guy. That's less LAMF and more idiocy.

Yes, the very clear legislation was that British citizens resident in the EU at the time of Brexit retained full residency rights. The current Swedish government is choosing to ignore the law for some reason.

If the advice given from the tax agency is in writing, then that's an open and shut case in my view. He was told he didn't need to do anything, and believed them.

He basically fucked up and didn't do the right thing or find the right answers. Plenty of people managed to secure residency or even better citizenship in EU countries after Brexit.

Nah, this isn't it, bud.