The Beauty, Age, Goodness(badness), Size convention is a simplification of a more nuanced rule.
Adjectives which are subjective/figurative are placed before the noun. Adjectives which are objective/literal are placed after the noun.
Bon when used to refer to a man who is a good conversationalist would be a subjective/figurative use and therefore would be placed in front.
Bon when used to describe a man who has just received an award as a good man for his obvious charitable works in the community would be an objective/literal use and would therefore be placed after the noun.
Adjectives relating to Beauty, Age, Goodness and Size tend to subjective/figurative in nature so the B.A.G.S. convention is a handy way to make decisions about placement.
Adjectives are subjective by nature so there is always lots of room for discussion of this rule even amongst accomplished French speakers.
There is nothing the phrase used in this question to tell which category bon falls into so either use should be accepted. However most times bon will be in front. Perhaps Duo wanted to force students to find out that there are exceptional uses. Getting their answers marked wrong will cause them to look further to find out why. To that end here is why: http://french.about.com/od/grammar/a/adjectives_fickle.htm
I hear crying owls all over the place.
I'm sure that in ordinary conversations individual speaking styles will reflect ease of pronunciation.
I mean no one is going to stop you and say ...hey wait a minute.. Are you saying that everyone really, really knows that he is a good man or that everyone really, really believes that he's a good man.
Unless you are taking an exam, of course. Then it might be important for you to know the difference.
In English we might say he does good works. That does not mean (usually) that he is good at doing works but rather that the works he does are considered good for others. However that still would be an uncommon although valid usage of good.
Duo is not constructing phrases for you to try as many valid but rare applications of given words as possible. bon means more than just kind but you are correct that kind is a meaning that bon does carry. If Duo allows you to use kind for bon then for all they know you may think the terms are interchangeable which they are not.
If you wrote that someone was good at swimming anyone reading that would be very unlikely to think that you meant that the person was very kind when swimming. Kind is almost always good but good very often has nothing to do with being kind.
Duo wants to be sure you understand that.
You are right, but if you wanted to be specific, for "these" you could write "Ceci est" and for "those" you could write "cela est", but be careful, "Ceci, ce sont....." and "Cela, ce sont....." http://www.larousse.fr/dictionnaires/francais/ceci/13957/difficulte
Also, there are pronouns for this one and that one "celui-ci" and "celui-là" masculine version, "celle-ci" and "celle-là" feminine version,
"ceux" and "celles" in plural masculine and feminine. http://www.larousse.fr/dictionnaires/francais-espagnol/celui/648387?q=ceux http://french.about.com/od/grammar/a/pronouns_demonstrative.htm