You are missing the point... it's a random comment, it isn't directed towards anyone particular. The only person that seems to have even noticed it is you.
If he were to say (insert name here) is retarded, that would be offensive. This is extremely general, and therefore, it isn't.
And being a newbie does make a diference in this instance and pretty much all instances.
You aren't as aware of the mood in this community because you are new to it. We aren't fact giving machines, there is a bit of humor/personality injected into everyone and their signatures/posts.
Long story short, you can't please everyone. Hundreds of people will see a simple quote and think nothing of it while one person will see it as something offensive. You just happen to be that one guy.

Respectfully, I won't comment on the poster's past feedback but it probably has more to do with asking "stupid questions" and his interaction with others and absolutely nothing to do with a tag line.
I'm not defending anyone here, it's just it seemed to me that you were making a personal comment based on your past dealings with him or past perceptions of him, and using the tagline as an excuse to knock him down a peg.
That's not cool.