I'm not sure what you mean when you ask, "where from I can know about the rule" because the first Codex page you linked talks about, "Soliciting professional (for pay) assistance".
Because I wrote OP about Free help, not paid. Offering paid is not allowed.
It was an exceptional case, that was the reason to ask the student to contact. Normally Codex help page would work for normal case. Otherwise who will take the headache of others' via email, to be honest.
Anyway, this out to be discussed within your own thread.
"Topics and their discussions must be related to WordPress and providing support for users of WordPress. All other topics are subject to closing or deletion."
I am not WordPress user in this case, instead a solution provider. It has no direct relationship with WordPress software but the problem is becoming the fine line of difference of a regular supporter and just a member.
Openly I can not say - email this person, I telling him your issue to fix. I have some administrative connection with the main domain ! Thats why I wrote - "Never use same username everywhere, even do not disclose it." The person is basically using exact username and exact number of password characters in most places. When he said SCAD, I simply logged in. Otherwise I how I will know that the use same username everywhere and warn him not to disclose it publicly.
I wrote a bit in a generalized way in my previous reply.