Correct.
OP, Please do not rely on the following as legal advice, because I am not a lawyer and I do not represent you in a court of law.
Citizens' Arrests in California - basic rundown of required elements and definition, with relevant linkage to more
The choice at this point for you is whether or not to file a police report, which is what the landlord should have told you to do as it is simple common sense. Should you choose to file a police report for assault, you may be asked to give testimony under oath. The longer you delay it, the less credible it would be (layperson's opinion).
In California, if you make a citizen's arrest, you must report the incident to the police in full and turn over the perpetrator as soon as you possibly can. That should be a matter of minutes in most cases; otherwise it's false imprisonment/kidnapping, and the perpetrator could press charges for that. The police would likely interview you, under which circumstances you could invoke your 5th Amendment rights (meaning you need not incriminate yourself) - but if the person who assaulted you goes to trial or even before, you could be subpoenaed to give sworn testimony.
Short version: not an optimal situation; keep yourself out of it as best you can, and if you choose to pursue an action, keep your own hands clean.
Good luck whether you decide to pursue the action or not.