There is a master
sshd process that listens to incoming connections, and in addition (for recent versions of OpenSSH) there are two processes called
sshd for each incoming SSH connection, one running as root and the other running as the logged-in user. If your OpenSSH is compiled without privilege separation (I don't know whether that's supported on AIX), there'll be a single
sshd process per connection in addition to the main one.
You must have killed either a per-connection
sshd or the master process, but not both. If you can still logged in over SSH, then what you killed was a per-connection process.