Because the grammar is incorrect.
It should be "him and his wife" as you correctly say.
This is probably an example of hypercorrection. The speaker has been corrected at some time for using 'him' instead of 'he', e.g.
"Him and me did it."
This is probably an example of hypercorrection. The speaker has been corrected at some time for using 'him' instead of 'he', e.g.
"Him and me did it."
He has misunderstood the grammatical rules, over-generalised and gone to the other extreme.
