OK....let's try for an example that might illustrate what I'm talking about.
FB friends are judges for a Macarena competitions (you know, the funky dance thing from the mid 90s?). Way back when, when the Macarena competitions were invented, there was also a certain offshoot of the competitions where you actually had to play the Macarena on a drum set. Macarena competitions start with teams of children and progress to older ages. Only very large competitions still do both aspects, or sometimes the playing aspect is only included at advanced levels, like for adults who have been doing this since they were children. For both aspects, there are rules to judge the performances, but obviously they are very different disciplines and thus, the criteria on which to judge them is very different. Typically, if you're a dancer, you don't play, and vice versa. So even though they both involve the Macarena, they generally don't overlap.
I got to know both of these people through Macarena dance competitions about 6 years ago. However, I've been involved in the sport of Macarena playing for almost as long, and am one of the few in our area who know something about the discipline. They both know that I'm really into Macarena playing.
Both of the people had apparently just taken the certification exam so they'd make sure that they were current on the latest and greatest rules for judging Macarena competitions. Since this is primarily geared toward the Dance aspect, and they only ever judge the Dancing, the Playing is out of their area of expertise. On their FB walls, they remarked that they'd just taken the exam and really hated the questions about judging the Macarena playing. I simply asked what types of questions they were. It wasn't something where I'd be able to research it for myself unless I went through the entire training that they do when someone wants to be certified as a Macarena judge (which I don't and can't, for other reasons). So I was just curious as to if they were in-depth questions or just something general that someone with very little knowledge of the playing aspect would be able to deduce and answer.
It seemed to be a very mundane question, yet one that was DIRECTLY related to both of their posts, since they brought it up in the first place! So that's what struck me as odd about (first) not getting any sort of response, and then (second) finding that my comment had disappeared.
Hope that helps with understanding.
And now I think I'm off to download the Macarena and do some Macarena cardio.