If the bouldering tag is justified in this case, how so, and would not that logic allow gross over-tagging by any related topic?
The below comes from completely personal opinion and my experience of working as a rock climbing instructor for a little over 3 years, and my desire to make this stack exchange as awesome as possible.
I think part of the bigger issue with
Rock-Climbing is not actually
Bouldering but the
Rock-Climbing tag. Everything tagged
Bouldering can be tagged
Rock-Climbing as well.
Bouldering is one of 4 major subsets of climbing, the other 3 being Ice, Sport and Traditional (trad). All 4 require different sets of gear and to some extent different techniques. Also, there are somewhat few outdoor areas that are setup for sport and trad, and while you could boulder at those areas, there are usually better places to go if all you want to do is boulder.
I think the bigger issue is not
Bouldering tag but
Climbing tag and
Rock-Climbing tags. Should they all be rolled into one or should they be separated and specifically defined somehow?
Also, about the finger pain after climbing I don't think directly relates to bouldering. The content of the question could pertain to any form of technical rock-climbing, and other than the tag doesn't specifically mention anything that is unique to bouldering.
I'd go one of 2 ways. Either have one all encompassing tag
Rock-Climbing and no subset tags, or all subset tags and only allow them to be used when the question specifically pertains to that subject. In this second form, a question about a carabiner is not specific to any one subset (being used in Ice, Sport and Trad) so it could only be tagged Rock-Climbing but a question about nuts could be tagged trad.
On the first, finger pain after climbing directly relates to bouldering, so I think at this time it's appropriately tagged.
On the second, the logic does not follow that if we allow this one question to be tagged in this way then there will be rampant and gross over-tagging. It's kind of a "But where will it END" slippery slope argument.
There are going to be areas with lots of overlap, but which do have distinctions. Over time we may find that bouldering is a superfluous tag, but right now I think we should leave it for search engine stuff. It's logical that someone bouldering may be looking for finger pain help and find these answers useful.
So far, no one stands out as a above-and-beyond expert on the bouldering topic. If we do keep the tag then we'll want to consult someone with a high rep in that tag (and other climbing topics) to help trim it down. I'm hesitant to start heavily tag policing gray areas until we have more community activity. So, unless there's evidence that this is either discouraging traffic, or discouraging climbing experts, I'd leave it.
Lastly, there's only 5 total questions tagged as bouldering. I'd wouldn't consider that some sort of gross over-tagging epidemic.