Martha is right. For the sake of those reading topics now or later, it can be a bit distracting to have discussions running in multiple directions at once and information scattered all over the place.
In a perfect world all discussions would remain rigidly (and potentially boringly) on-topic, but we know that's never going to happen - especially with cavers. If we catch a discussion running astray early enough, we often will split it into separate topics. But that's a fair amount of work, and the result can be quite disjointed. Ideally the original poster and/or those who reply would say something like "blah blah blah, and incidentally this reminds me of blah-blah so I will start a new topic here" (with link). But of course we don't live in an ideal world, and the moderators can't always be cleaning up after everybody.
Many of us regular forum members (and moderators) read virtually anything and everything posted in all sections of the forum. But there are others who deliberately ignore sub-forums which are unimportant to them, and only read relatively few of the many subjects of discussion. I suspect Bob falls into this category, and decided to express his frustration about this photo/video forum topic which has turned into a contentious discussion about unrelated carbide allergies.