IANAL, but I think that in this context "legal advice" has a meaning beyond the English one. It is also used to indicate an attorney-client relationship and the associated liability and confidentiality.
So someone can give legal advice (English), but say it isn't legal advice (Legalese) and that makes it not legal advice (Legalese).
The main reason for IANAL, TINLA is that lawyers have attorney's immunity, and joe shmoe does not. If somebody relies on my opinion as if it is legal advice and from the circumstances it looks like legal advice, I can be in deep poop if the advice was wrong.
So someone can give legal advice (English), but say it isn't legal advice (Legalese) and that makes it not legal advice (Legalese).