I must have missed the bit of the CASA FOI Duty Statement that includes bodyguarding and bouncing duties in the foyer of a multi-tenant office building.
Two people on one, and the two people came to the one in the foyer of a multi-tenant office building during business hours. Until the two arrived, the one was a threat to nobody, so far as I can tell. And there were multiple witnesses and a security camera.
The simplest and most obvious reason why the one was not prosecuted for assault is: The one assaulted nobody. A self-appointed bodyguard/bouncer tried to intimate the one, but the tactic failed.
And I very much doubt whether CASA has the authority to decide who is allowed and not allowed in the foyer of a multi-tenant office building during business hours. That would probably the decision of the building owner, not individual tenants.