I took a look at the marriage. It doesn’t say he was born in Kansas. It says
“Alfred Brown, of Kansas City and Matilda Auger of High Wycombe , England “
The marriage took place in Kansas City Oct. 11, 1873
I would think this meant his usual residence at the time was Kansas City and hers was High Wycombe.
Perhaps he had been living there for some time and she had recently arrived from England.
I’ll see if I can find passenger lists for them.
In 1871 London, England census Matilda Auger age 19, born West Wycombe is living with cousins
Nadie 37 , civil engineer, born Marylebone, London
Mary Matilda, 31, wife , born West Wycombe
Matilda, 19, cousin, born west Wycombe
In the image his name looks like Nath’l to me
So Matilda must have gone to US after this census and before Oct. 1873 marriage