We're looking at is households, and the easiest way to explain this jump is actually that the economy is more fucked than ever and more working age people are living together. If we consider the type articles you're referencing, that have been noting the migration of young, educated, working-age adults back to their parents homes in the USA-- we should very well expect to see a large spike in the reported median household income. The same growth would be true if more people were living in situations with roommates where ideally they wouldn't.
Here's the definition of a household from the linked article:
> A family household is a household maintained by a householder who is related to at least one other person in the house-hold by birth, marriage, or adoption and includes any unrelated individuals who may be residing there. A nonfamily household is a householder living alone (a one-person household) or sharing the home exclusively with nonrelatives.
Addendum: I'd like to note, that even if household size itself appears to be low; that's likely due to reproduction rates being on the decline as more people, on average, are having smaller families each year...