I can't read the article, but it seems like the legal concept of community property (Spanish civil law) vs. separate property should somehow factor into this discussion. About one third of the U.S. married persons are domiciled in community property states (CA & TX being the two largest by population).

Commingling separate funds in a joint account can transnmute them to community property.

https://www.irs.gov/irm/part25/irm_25-018-001