That's not at all accurate. Sub domain or sub-hosts can be an A record, or a CNAME, there is no required standard for it. As long as it points to the correct place it will work fine.
A CNAME can be used if the record shares the IP address of the main server by using the @ symbol, but again, there is no requirement to use either or.
A CNAME can be used if the record shares the IP address of the main server by using the @ symbol, but again, there is no requirement to use either or.