Thank you for posting this, @Jiannina Camillo, I may fire off a submission on the basis that I fit their minority criteria by coming from "a socio-economically marginalised background"—meaning, I'm dirt poor!
Hachette's inclusion of impoverished working-class folk is part of a trend by agents and publishers to encourage unknown writers, who don't have the funds to attend pricey writing courses. Award-winning British novelist Kit de Waal is doing good work by funding a creative writing fellowship. She edited an anthology of working-class essays, poems and memoirs called Common People. This is all to the good, for writing, reading and the world of publishing can appear elitist, a closed shop which bars anyone without a university education. It's little wonder that reading is in decline, when most stories are not about the lives of ordinary people or written by authors from minority groups.
What's really unusual about Hachette's submission rules is that they say they want a synopsis and a "three-thousand-word sample of your writing." That implies the sample can be from anywhere in your book—not just the opening 3,000 words, as is usually requested. In six years of querying, sending off almost 700 submissions to about 150 different agents and publishers, this is only the second time I've seen such a thing.