Yes, one confusing aspect of SMTP is that there is a server-server part (listening on port 25) and a client-server part (465 or so, usually authenticated). I haven't dug in-depth, so maybe they are exactly the same protocol though.
Acessing port 25 of server is usually blocked by ISPs as a way to prevent spam.
The difference in ports is due to SSL/TLS expected to be automatically applied on 465 iirc like 80/443 for HTTP(S) (you can also encrypt 25 by issuing STARTTLS after setting up a connection but it's not the default and might fail I think).
Authentication with mail is separate, usually to allow for relaying whilst anyone can usually drop emails IFF your server is the destination.
Confusing and needlessly complex? Yep. Natural result as of uncontrolled evolution? Yep.
Acessing port 25 of server is usually blocked by ISPs as a way to prevent spam.