Hmmm ... I didn't think that rb49's was implying anything about your ability to understand things, so much as he was pointing out that Dr. Drib has a right to choose to add emphasis to his own
comments in an effort to make them clearer to those reading them (though, I grant you, he might have phrased it a bit more ... gently).
I usually use italics for that: when I want to be more clear in the written word than I could without them. I do tend to avoid using bold, personally, because, as you pointed out, it's gotten to where it's read as more emphasis than I usually mean
I agree that Dr. Drib overdid it a bit with the bolding in his comment, and that italics might have been a bit better choice for most of it, but there may have been a ... gentler way to point that out to him. In any case, he's recognized that he unintentionally offended, and apologized, for doing so, so there you go. If you ignore the bolding (now that you know he meant it differently than folks usually do), his comment reads a lot differently than it does with the bolding.
While you and I and rb49 already know about bolding and italics and all caps (to toss that one in with its brethren), there's a reasonable chance that there are others reading this who are newer to the topic and appreciate the information so that they don't go about inadvertently 'yelling' at other folks when they just mean to emphasize what they're saying, or who just haven't yet considered the implications of the various typesets in this venue.
In any case, I think you're right that this thread has probably served as much as it can, we know you're working on a collection of Twain's short stories (excellent choice, by the way!). Dr. Drib knows better how others will read bolded text, and that he shouldn't over-do it unless he means
to be yelling at folks. You know that there's a thread dedicated for sharing what projects are underway, so you can better coordinate with the others who are working on book projects. And any newbies that happen along will learn a bit about communicating better in this bewildering cyber-world, knowledge that they might have had to learn the hard way otherwise. All in all, not a bad set of accomplishments for such a short thread.