Was your account actually closed or did you get a suspension? If you were suspended for a chat offense then Advertising in LFG can certainly be a cause.
Players have never been allowed to use LFG to advertise services. In Retail it has to be in Trade Service. In Classic you had to use Trade, although recently they did open a Trade Services channel for some versions.
Advertising any services for gold outside that is a chat violation. Those start with a week Silence, then a week suspension, and go up from there for each offense.
Here is the article.