Is Zihar mentioned in classical arabic dictionaries/works that did not take it from hadith?
I don't know as I've never looked into that.
It seems the article is claiming that it was only in the hadith...
They say "hadith literature defines zihar as". They never explicitly say it's only mentioned in hadith and not classical arabic dictionaries/works (i.e. non-hadith).
"..and they specify a dictionary which has taken it from the hadith.
Can you provide a quote from the article?