You're absolutely correct -- "scare quotes" are an element of American English, not British English. In this context, they're simply indicative of the fact that somebody (not the paper) has called these workers "slaves".

Two countries divided by a common language, as they say. When I moved to the UK from America, this was admittedly one of the more confusing points of differentiation for me.

American newspaper headlines often use quotes in this way too. And those are often mistaken for scare quotes as well.

(American) Usually when I see it intended as a quote in the headline, the "says X named official" is either in the headline or in the lede, which will basically just be an expansion of the headline anyway. Often though, that's not the case, and there's palpable sarcasm associated with the quote. (I've come to dislike that style of writing stories.)

I associate that style of writing more with magazines than newspapers, though I suppose I don't read a lot of physical newspapers these days and maybe there is a plague of sarcastic headlines on news articles that I'm just not aware of.

I don't read printed newspapers, but do see it a lot online. I haven't noticed any particular sources which seem to be rabid abusers (other than the obvious, like rt and fox, which I ignore anyway).

Ah okay, that makes more sense. I tentatively revoke my criticism of the author and/or editor if that's what is going on here.

That seems to be the case here, although it's slightly more confusing (to me, an American reader) when it's only a single word in quotation marks.