Hi Alessio,
I believe you might need the ‘OR’ secondary logic instead. I am not sure if that will return only the one result, as the xProfile fields are all separate fields, and the keyword logic applies on each field separately.
I think ACF has a feature to add user meta fields, I think that should work. You should maybe try creating 1 or 2 fields for testing, but as far as I know, ACF uses regular user meta, so that should be okay.