You posed a question that could not be answered because it treated "E-numbers" as if it was one coherent group of chemicals. The closure and answer pointed that out, but did not do so in a hostile way. You still felt that it was hostile, because it is a normal human reaction to feel that you yourself has been attacked/insulted/degraded when you are told that you are wrong.
But it is very important for skeptics to accept when they are wrong. In my opinion it in in fact the most important part of being a skeptic, as you otherwise cling on to beliefs even when they are disproved, which isn't very skeptical. :-)
We can't allow ourself to get angry when told we are wrong. We are skeptics. It's our business to find all the incorrect assumption and point them out. Even when we ourselves make those incorrect assumption.
I think we will see a lot of these kinds of reactions here. This site is about skeptics, it is people who come here asking a question about statement "X" because they believe something about it. They may believe it's false, and they may believe it's true. And sometimes they will get their suspicions confirmed, and sometimes they will be told "no, you were wrong" and sometimes they will be told "You misunderstood something and your question is incorrectly posed". And most of these peoples immediate reaction will be "Oh, that is SOOO rude!" Because that's how people are, and that is how we react.
But as skeptics it's important that we always at that point remember to step back and look at things objectively. Was the other guy rude, or did he just explain to me that I was wrong? Is my indignant reaction correct?