Yep I think @kbickell is spot on. It looks like this is the way they just happen to configure their particular installations. Given that it is self hosted (and quite flexible) there may be a reason for this.
I will admit I am only just starting to play with the Self Hosted version to try to learn a little about it, so it is entirely possible that this is a standard for all self-hosted installations, though I would find that unlikely.
You may want to ask them specifically if the 'Site Admin' is an option that they set up differently to the default out-of-box self-hosted installation, and if so, what the specific reasoning is. While this won't change anything, it may help for you to know the reasoning and for which cases you should use the different accounts.
I will also put out the possibility that this is standard for Canvas, and for hosted installations by Instructure, we simply do not need or see the Site Admin sub-account.
Glad they were able to help out, but if you are curious, never hurts to ask more questions.
Cheers,
Stuart
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