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
I think the bigger issue is not
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
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.