From the Smithsonian article:
"Warily, the three strange figures approached and sat down with their visitors, rejecting everything that they were offered—jam, tea, bread—with a muttered, "We are not allowed that!" When Pismenskaya asked, 'Have you ever eaten bread?' the old man answered: 'I have. But they have not. They have never seen it.' At least he was intelligible. The daughters spoke a language distorted by a lifetime of isolation. 'When the sisters talked to each other, it sounded like a slow, blurred cooing.'"
It was the Lykov family, members of the pre-Bolshevik Russian Orthodox church. When the Bolsheviks overtook Russian, Orthodox believers fled to the mountains - and apparently, some of them fled deeper than others. This family was discovered hundreds of miles from the nearest human habitat. They had been holed up on a homestead farm for 40 years,m and had completely missed world history from 1936 to 1978. They had noticed the satellites in the sky at night, but concluded that "People have thought something up and are sending out fires that are very like stars."
And the matriarch of the family is the only surviving member today. Here's a video interview with her, although you'd have to translate from the Russian.