Looks that way. See the following:
root@swi-mdm9x28-wp:~# nc 192.168.2.3 7777
nc: can't connect to remote host (192.168.2.3): Connection refused
root@swi-mdm9x28-wp:~# nc 192.168.2.3 1883
^C
root@swi-mdm9x28-wp:~#
The first attempt uses a bad port number 7777 so it’s refused. The second attempt connects. This indicates that your broker on Ubuntu is OK to receive connections from the WPxxxx.
This means that if your application on the WPxxxx won’t connect to the broker on Ubuntu it is probably doing something wrong.