When the client is initiating a data transfer, it asks the FTP server, where to connect to. The IP address that you server provides is likely its internal address on its network, rather than an external IP address that can be used by the client. It's an incorrect configuration on the server-side.
But as this is a quite common misconfiguration, many FTP clients, including FileZilla, can workaround it. They simply ignore any IP address the server provides, if it's unroutable from the client's network location, and use an FTP server address instead. That's what happened.
See my recent answer for explanation of the passive mode architecture.
Regarding the certificate accepting: As you did not share with us, what was the reason given by FileZilla to ask you to accept the certificate, we cannot really help you.