MySQLi and SSL connections

Nope, it's the client that falls back to an unencrypted connection if the SSL one fails. And that's written on the very page you've linked:

For MySQL client programs, the --ssl option is used as follows:

...

   - Before MySQL 5.7.3, --ssl is advisory: --ssl permits but does not require the client to connect to the server using encryption. Therefore, this option is not sufficient in itself to cause a secure connection to be used. For example, if you specify this option for a client program but the server has not been configured to support secure connections, the client falls back to an unencrypted connection.