On my Mac (MacOS - Ventura 13.3.1) in Apple Contacts I have some personal contacts that show up as businesses in my business smart list.
Example -
I have this contact formatted as follows (Company field is blank. Company box is unchecked):
I have the following Smart List:
When I go to my Smart List “Business”, Mr Bleaux shows up as a business. I have many contacts that do the same. Anyone else notice this behavior?
It struck me as odd that the full name is on the same line in the contact listing. And that made me wonder if perhaps you have the first name and last name (surname) in a single field, rather than two fields. I have seen that cause a contact to be considered to be a business/company (presumably based on the reasoning that a business only has one name while a person has at least two). Try editing the contact so the first and last names are in separate fields and see if that fixes the issue.
I just checked all of the contacts where this is happening and the names are all in two separate fields. Good thought, though. Thanks for your help. I will fix all of the contacts individually. I guess I may never know why it happened. 
