In any case, I see this poster as a cheat sheet: not something to learn from, but a quick reference for someone who has already done their homework and learned about those logical fallacies.
Argument from authority -- It is important to note with this fallacy that authorities in given fields may very well have valid arguments, and that one should not dismiss another's experience and expertise. To form an argument, however, one must defend it on its merits i.e. know why the person in authority holds the particular position that they do.
Only vaguely. You don't actually have to know what general relativity is or how it works to form an argument based on the statistical likelihood of physicists being correct. You don't really have to know "why" the person in authority holds their opinion, only that they are both an expert on the topic they are covering and that there is a general consensus among other experts on the same topic.
It is, of course, entirely possible that the opinion of a person or institution of authority is wrong; therefore the authority that such a person or institution holds does not have any intrinsic bearing upon whether their claims are true or not.
I'm not sure what this is trying to say, but there's certainly justifiable basis in believing that person's authority has an intrinsic bearing on the probability that their claim is true.
How is the quoted definition at all useful -- to either logicians or laymen?