yeah, the off-topic section is from all stardock forums
Not quite *all* yet but getting closer every day.
Actually there are 2 such forums that are similarly named. One is "Off-topic" (this one, /forum/412) and there's also "Off-Topic (note the capital T, /forum/349) neither of which is yet accessible from https://forums.wincustomize.com although both are newly accessible from https://forums.joeuser.com.
Four months ago the "Off-topic" (/forum/412) forum was accessible only from the Demigod, Galciv2, Impulse, Sins and Stardock sites, since then I know Joe User has been added, perhaps others. Similarly the "Off-Topic (/forum/349) was only accessible from the Galciv2 and Stardock sites and in both cases seems to be a Galciv2 specific off topic forum since in both cases it is a subforum of the "GalCiv II" forum.
Interestingly enough on Joe User both of these forums are obscurely placed together as subforums under the "Misc" (/forum/17) forum and so it's unlikely that anyone there would intentionally post a thread to that forum however since any activity causes threads in these forums to scroll by on the recent posts list, replies from Joe User will probably be common.
The point is that you really do have no clue *where* a post or reply is coming from. I probably know as much about SD's forum structure as any non Stardock employee having exhaustively checked out 755 forums spread out over 11 sites of which 373 were unique, but like I said my information is at least 4 months old. Since then a new forum site has been added (https://forums.elementalgame.com) as well as an unknown number of new forums added and, as as we have seen, access to existing forums have been expanded to sites where they were not previously accessible.