https://wiki.mikrotik.com/wiki/Manual:Console_login_process
If you telnet from the client then the TCP session id from the client IP address to the router IP address.
If you use the telnet tool from the router, then the telnet TCP session is from that router IP address to the destination router IP address. This way you can hop from one network to another network that the client cannot reach itself.
The TELNET tool in RouerOS can connect to the MAC address of a RouterOS router, not using TCP/IP connectivity.