Member Rara Avis
I don't think there's anything intrinsically rude with using a quote to make a point. It would be no different than if I said "A rose by any other name…" and then let you finish the thought (assuming my quote was germane to your post). Since you don't really know the intent behind the quote, let alone what is was to have meant, it's a little hard to call it rude.
Yes, opinion and advice are two different things. But the differences are darn subtle. Do you know of any possible way to give advice without also giving an opinion? When you give someone advice, you are telling a person what you think they should do. What you think they should do, however, is just an opinion (though some are more solidly based than others). If you ask for advice you will always get an opinion. It's up to you whether you want to take that opinion seriously.
Of course - that's just my opinion.