This category is populated by articles transcluding {{Infobox person}} with potentially multiple people after the | spouse = parameter.
The template code contains logic to dynamically change the label to appropriately display "Spouse" if only one person is listed or "Spouses" if multiple people are listed in any of the typical list templates (e.g. a Plainlist or Unbulleted list).
If the template logic cannot definitively determine a singular or plural set, it will display as "Spouse(s)" to remain neutral if it is not clear.
The template logic may assume a comma is separating two distinct people, but the comma may be part of that person's legal name (e.g., some people use a comma before a Jr. or Sr. suffix: "Alex Aardvark, Jr.").
A workaround to force the template to recognize the singular person is to add {{Force singular}} after the name/argument.