When a host is booted on a network which MAAS controls the machine goes into enlistment which gathers basic information about the system. If an IPMI, HP Moonshot, or Facebook Wedge BMC is detected MAAS creates its own user to interact with the BMC. It appears MAAS is detecting that the IBM Server X3650 M4 is using an IPMI BMC and has configured it with a MAAS username and password.
A rack controller must be on the same network as the BMC. You can test this by SSHing into the machine running the rack and executing the following command
$ ipmipower -s -D LAN_2_0 -h 192.168.70.125 -u maas -p l005vVhVl2
The MAAS logs may also provide more information, they are available in /var/log/maas