You should clarify that in Russia they operate in "living space" sq.meters, meaning that 400 sqft will not include kitchen, corridors, bathroom, etc. Just the bedrooms and the living room.
Secondly, you are over-generalizing. While a part of population did in fact live in cramped conditions (or even in shared condos, whereby 2+ families shared a single apartment), more than enough people lived in a very decently spaced apartments, with living space ranging between 28 sqm to 40-50 sqm. So "400 sqft" apartments were nowhere close to being "luxury".
OTOH, a bathroom with a window - now that was indeed a true luxury (because how the vast majority of buildings where designed).
We definitely had company over, often gatherings of 10-12 people and one time we had 5 overnight guests (that was a bit crazy but fun).
Also, in the sentence about the coffee table (seen two photos up), shouldn't that be "second photo from the top"? Unless I misunderstood and tried to find a coffee table in the photo with the surfboards/piano
Edit: it was in the picture with the surfboards. It is the blue trunk in the lower left. Coffee table/trunk/changing table
My parents went through it in 80s. By then this mostly worked for military/otherwise connected families, but has broken down for the rest of the country with wait list numbering in years. In theory you gave up smaller apartment for a slightly larger as need arose. In practice, most families did not want to move far and construction pace did not keep up for economic reasons.