a lot of times this can happen unintentionally— these systems can coopt the primary ethernet port when the dedicated one is unplugged and many default to this behavior
For example a lower end Dell without a separate iDRAC port will share with the first NIC with a IP that is either DHCP assigned or a built in default - both of which are unlikely to be forwarded by accident.
Older Dells had a standard root password of "calvin" which was an appalling idea. Newer ones do as HPE and have a default autogenerated monstrosity printed on a pull out slide. Also you can set jumpers on the mainboard to reset it. Look at the manual or the inside of the cover.
I insist on a certain boot order from the factory and have the initial pxe boot of the server lock down the idrac. It isn't perfect but it beats having someone pull and scan all those tags.