"...her fiancé Serhiy Lobanov was asleep on a mattress in the kitchen."

That's some Soviet shit.

My wife grew up in a one-room apartment with her parents and two older brothers.

I routinely tell her "I want our daughter to have everything you didn't get as a kid".

In the USSR, you usually don't have a spare guest room. An unmarried young man would be lucky to live in a separate apartment; otherwise, it is usually just a bed in a dormitory. At best, it is a one-room (12-20 m2) apartment with a kitchen (10 m2). A hotel is too expensive, so you put your guests into your bed, a folding chair, or a folding cot and go to the kitchen to sleep on a mattress. There were families of 4-5 people who lived in such apartments permanently.

Even in the US, I don't know many friends with enough living space to have an entire spare guest room. When friends visit, they sleep on the living room couch or an air mattress. Is this not typical?

To be fair it says "In a nearby apartment packed with guests" - if your house is oversubscribed, the host gets the worst accommodations is pretty common worldwide - "He had a horrible thought that the cakes might run short, and then he—as the host: he knew his duty and stuck to it however painful—he might have to go without."