Sam's Story is based around something Homer says in Metro 2034.
In Metro 2034, homer mentions the town of vladivostok being powered by a nuclear submarine that survived the war.
If you didn't know, its the exact place and submarine where Metro exodus: sam's story takes place.
Metro 2034 pg 191
"Right, and what about the submarine?' His rival drawled. 'The nuclear submarine that was on a long-range mission, and when the strikes and counter-strikes began, it simply didn't have enough time to move into battle position. And when it did surface, everything had already been over for ages. So then the crew put it on permanent mooring not far from Vladivostok...' 'And to this day an entire village is powered by its reactor,"